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    關於樹的資料結構其實有很多種，常見的結構有二叉平衡樹、b樹、b+樹。這中間b+樹用的尤其多，特別是檔案系統方面。因為大家都知道，對於fs的node而言，我們必須儘可能使用到page裡面的每一個bit，畢竟page的載入其實是非常花時間的。

    網上能找到、可用的b+樹程式碼不多，下面這份程式碼也是通過wiki找到的，原來的地址在這。其實不管什麼操作，都要包括初始化、增加、刪除、合併、拆分這幾個操作。下面的程式碼是一份完整的操作，大家可以按照提示一步一步操作，應該收穫很多。

    程式碼可以用gcc編譯。執行的時候，可以帶兩個引數。第一個引數表示每個節點可以帶的子節點數，第二個引數是file檔名，其中儲存了可以排序的資料等內容，注意每一行表示一個數據。

/* 
 *  bpt.c  
 */
#define Version "1.13"
/*
 *
 *  bpt:  B+ Tree Implementation
 *  Copyright (C) 2010  Amittai Aviram  http://www.amittai.com
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *
 *  Author:  Amittai Aviram 
 *    http://www.amittai.com
 *    
 
[email protected] or [email protected]
 *    Senior Software Engineer
 *    MathWorks, Inc.
 *    3 Apple Hill Drive
 *    Natick, MA 01760 
 *  Original Date:  26 June 2010
 *  Last modified: 15 April 2014
 *
 *  This implementation demonstrates the B+ tree data structure
 *  for educational purposes, includin insertion, deletion, search, and display
 *  of the search path, the leaves, or the whole tree.
 *  
 *  Must be compiled with a C99-compliant C compiler such as the latest GCC.
 *
 *  Usage:  bpt [order]
 *  where order is an optional argument
 *  (integer MIN_ORDER <= order <= MAX_ORDER)
 *  defined as the maximal number of pointers in any node.
 *
 */

// Uncomment the line below if you are compiling on Windows.
// #define WINDOWS
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#ifdef WINDOWS
#define bool char
#define false 0
#define true 1
#endif


// Default order is 4.
#define DEFAULT_ORDER 4

// Minimum order is necessarily 3.  We set the maximum
// order arbitrarily.  You may change the maximum order.
#define MIN_ORDER 3
#define MAX_ORDER 20

// Constants for printing part or all of the GPL license.
#define LICENSE_FILE "LICENSE.txt"
#define LICENSE_WARRANTEE 0
#define LICENSE_WARRANTEE_START 592
#define LICENSE_WARRANTEE_END 624
#define LICENSE_CONDITIONS 1
#define LICENSE_CONDITIONS_START 70
#define LICENSE_CONDITIONS_END 625

// TYPES.

/* Type representing the record
 * to which a given key refers.
 * In a real B+ tree system, the
 * record would hold data (in a database)
 * or a file (in an operating system)
 * or some other information.
 * Users can rewrite this part of the code
 * to change the type and content
 * of the value field.
 */
typedef struct record {
	int value;
} record;

/* Type representing a node in the B+ tree.
 * This type is general enough to serve for both
 * the leaf and the internal node.
 * The heart of the node is the array
 * of keys and the array of corresponding
 * pointers.  The relation between keys
 * and pointers differs between leaves and
 * internal nodes.  In a leaf, the index
 * of each key equals the index of its corresponding
 * pointer, with a maximum of order - 1 key-pointer
 * pairs.  The last pointer points to the
 * leaf to the right (or NULL in the case
 * of the rightmost leaf).
 * In an internal node, the first pointer
 * refers to lower nodes with keys less than
 * the smallest key in the keys array.  Then,
 * with indices i starting at 0, the pointer
 * at i + 1 points to the subtree with keys
 * greater than or equal to the key in this
 * node at index i.
 * The num_keys field is used to keep
 * track of the number of valid keys.
 * In an internal node, the number of valid
 * pointers is always num_keys + 1.
 * In a leaf, the number of valid pointers
 * to data is always num_keys.  The
 * last leaf pointer points to the next leaf.
 */
typedef struct node {
	void ** pointers;
	int * keys;
	struct node * parent;
	bool is_leaf;
	int num_keys;
	struct node * next; // Used for queue.
} node;


// GLOBALS.

/* The order determines the maximum and minimum
 * number of entries (keys and pointers) in any
 * node.  Every node has at most order - 1 keys and
 * at least (roughly speaking) half that number.
 * Every leaf has as many pointers to data as keys,
 * and every internal node has one more pointer
 * to a subtree than the number of keys.
 * This global variable is initialized to the
 * default value.
 */
int order = DEFAULT_ORDER;

/* The queue is used to print the tree in
 * level order, starting from the root
 * printing each entire rank on a separate
 * line, finishing with the leaves.
 */
node * queue = NULL;

/* The user can toggle on and off the "verbose"
 * property, which causes the pointer addresses
 * to be printed out in hexadecimal notation
 * next to their corresponding keys.
 */
bool verbose_output = false;


// FUNCTION PROTOTYPES.

// Output and utility.

void license_notice( void );
void print_license( int licence_part );
void usage_1( void );
void usage_2( void );
void usage_3( void );
void enqueue( node * new_node );
node * dequeue( void );
int height( node * root );
int path_to_root( node * root, node * child );
void print_leaves( node * root );
void print_tree( node * root );
void find_and_print(node * root, int key, bool verbose); 
void find_and_print_range(node * root, int range1, int range2, bool verbose); 
int find_range( node * root, int key_start, int key_end, bool verbose,
		int returned_keys[], void * returned_pointers[]); 
node * find_leaf( node * root, int key, bool verbose );
record * find( node * root, int key, bool verbose );
int cut( int length );

// Insertion.

record * make_record(int value);
node * make_node( void );
node * make_leaf( void );
int get_left_index(node * parent, node * left);
node * insert_into_leaf( node * leaf, int key, record * pointer );
node * insert_into_leaf_after_splitting(node * root, node * leaf, int key, record * pointer);
node * insert_into_node(node * root, node * parent, 
		int left_index, int key, node * right);
node * insert_into_node_after_splitting(node * root, node * parent, int left_index, 
		int key, node * right);
node * insert_into_parent(node * root, node * left, int key, node * right);
node * insert_into_new_root(node * left, int key, node * right);
node * start_new_tree(int key, record * pointer);
node * insert( node * root, int key, int value );

// Deletion.

int get_neighbor_index( node * n );
node * adjust_root(node * root);
node * coalesce_nodes(node * root, node * n, node * neighbor, int neighbor_index, int k_prime);
node * redistribute_nodes(node * root, node * n, node * neighbor, int neighbor_index, 
		int k_prime_index, int k_prime);
node * delete_entry( node * root, node * n, int key, void * pointer );
node * delete( node * root, int key );




// FUNCTION DEFINITIONS.

// OUTPUT AND UTILITIES

/* Copyright and license notice to user at startup. 
 */
void license_notice( void ) {
	printf("bpt version %s -- Copyright (C) 2010  Amittai Aviram "
			"http://www.amittai.com\n", Version);
	printf("This program comes with ABSOLUTELY NO WARRANTY; for details "
			"type `show w'.\n"
			"This is free software, and you are welcome to redistribute it\n"
			"under certain conditions; type `show c' for details.\n\n");
}


/* Routine to print portion of GPL license to stdout.
 */
void print_license( int license_part ) {
	int start, end, line;
	FILE * fp;
	char buffer[0x100];

	switch(license_part) {
	case LICENSE_WARRANTEE:
		start = LICENSE_WARRANTEE_START;
		end = LICENSE_WARRANTEE_END;
		break;
	case LICENSE_CONDITIONS:
		start = LICENSE_CONDITIONS_START;
		end = LICENSE_CONDITIONS_END;
		break;
	default:
		return;
	}

	fp = fopen(LICENSE_FILE, "r");
	if (fp == NULL) {
		perror("print_license: fopen");
		exit(EXIT_FAILURE);
	}
	for (line = 0; line < start; line++)
		fgets(buffer, sizeof(buffer), fp);
	for ( ; line < end; line++) {
		fgets(buffer, sizeof(buffer), fp);
		printf("%s", buffer);
	}
	fclose(fp);
}


/* First message to the user.
 */
void usage_1( void ) {
	printf("B+ Tree of Order %d.\n", order);
	printf("Following Silberschatz, Korth, Sidarshan, Database Concepts, 5th ed.\n\n");
	printf("To build a B+ tree of a different order, start again and enter the order\n");
	printf("as an integer argument:  bpt <order>  ");
	printf("(%d <= order <= %d).\n", MIN_ORDER, MAX_ORDER);
	printf("To start with input from a file of newline-delimited integers, \n"
			"start again and enter ");
	printf("the order followed by the filename:\n"
			"bpt <order> <inputfile> .\n");
}


/* Second message to the user.
 */
void usage_2( void ) {
	printf("Enter any of the following commands after the prompt > :\n");
	printf("\ti <k>  -- Insert <k> (an integer) as both key and value).\n");
	printf("\tf <k>  -- Find the value under key <k>.\n");
	printf("\tp <k> -- Print the path from the root to key k and its associated value.\n");
	printf("\tr <k1> <k2> -- Print the keys and values found in the range "
			"[<k1>, <k2>\n");
	printf("\td <k>  -- Delete key <k> and its associated value.\n");
	printf("\tx -- Destroy the whole tree.  Start again with an empty tree of the same order.\n");
	printf("\tt -- Print the B+ tree.\n");
	printf("\tl -- Print the keys of the leaves (bottom row of the tree).\n");
	printf("\tv -- Toggle output of pointer addresses (\"verbose\") in tree and leaves.\n");
	printf("\tq -- Quit. (Or use Ctl-D.)\n");
	printf("\t? -- Print this help message.\n");
}


/* Brief usage note.
 */
void usage_3( void ) {
	printf("Usage: ./bpt [<order>]\n");
	printf("\twhere %d <= order <= %d .\n", MIN_ORDER, MAX_ORDER);
}


/* Helper function for printing the
 * tree out.  See print_tree.
 */
void enqueue( node * new_node ) {
	node * c;
	if (queue == NULL) {
		queue = new_node;
		queue->next = NULL;
	}
	else {
		c = queue;
		while(c->next != NULL) {
			c = c->next;
		}
		c->next = new_node;
		new_node->next = NULL;
	}
}


/* Helper function for printing the
 * tree out.  See print_tree.
 */
node * dequeue( void ) {
	node * n = queue;
	queue = queue->next;
	n->next = NULL;
	return n;
}


/* Prints the bottom row of keys
 * of the tree (with their respective
 * pointers, if the verbose_output flag is set.
 */
void print_leaves( node * root ) {
	int i;
	node * c = root;
	if (root == NULL) {
		printf("Empty tree.\n");
		return;
	}
	while (!c->is_leaf)
		c = c->pointers[0];
	while (true) {
		for (i = 0; i < c->num_keys; i++) {
			if (verbose_output)
				printf("%lx ", (unsigned long)c->pointers[i]);
			printf("%d ", c->keys[i]);
		}
		if (verbose_output)
			printf("%lx ", (unsigned long)c->pointers[order - 1]);
		if (c->pointers[order - 1] != NULL) {
			printf(" | ");
			c = c->pointers[order - 1];
		}
		else
			break;
	}
	printf("\n");
}


/* Utility function to give the height
 * of the tree, which length in number of edges
 * of the path from the root to any leaf.
 */
int height( node * root ) {
	int h = 0;
	node * c = root;
	while (!c->is_leaf) {
		c = c->pointers[0];
		h++;
	}
	return h;
}


/* Utility function to give the length in edges
 * of the path from any node to the root.
 */
int path_to_root( node * root, node * child ) {
	int length = 0;
	node * c = child;
	while (c != root) {
		c = c->parent;
		length++;
	}
	return length;
}


/* Prints the B+ tree in the command
 * line in level (rank) order, with the 
 * keys in each node and the '|' symbol
 * to separate nodes.
 * With the verbose_output flag set.
 * the values of the pointers corresponding
 * to the keys also appear next to their respective
 * keys, in hexadecimal notation.
 */
void print_tree( node * root ) {

	node * n = NULL;
	int i = 0;
	int rank = 0;
	int new_rank = 0;

	if (root == NULL) {
		printf("Empty tree.\n");
		return;
	}
	queue = NULL;
	enqueue(root);
	while( queue != NULL ) {
		n = dequeue();
		if (n->parent != NULL && n == n->parent->pointers[0]) {
			new_rank = path_to_root( root, n );
			if (new_rank != rank) {
				rank = new_rank;
				printf("\n");
			}
		}
		if (verbose_output) 
			printf("(%lx)", (unsigned long)n);
		for (i = 0; i < n->num_keys; i++) {
			if (verbose_output)
				printf("%lx ", (unsigned long)n->pointers[i]);
			printf("%d ", n->keys[i]);
		}
		if (!n->is_leaf)
			for (i = 0; i <= n->num_keys; i++)
				enqueue(n->pointers[i]);
		if (verbose_output) {
			if (n->is_leaf) 
				printf("%lx ", (unsigned long)n->pointers[order - 1]);
			else
				printf("%lx ", (unsigned long)n->pointers[n->num_keys]);
		}
		printf("| ");
	}
	printf("\n");
}


/* Finds the record under a given key and prints an
 * appropriate message to stdout.
 */
void find_and_print(node * root, int key, bool verbose) {
	record * r = find(root, key, verbose);
	if (r == NULL)
		printf("Record not found under key %d.\n", key);
	else 
		printf("Record at %lx -- key %d, value %d.\n",
				(unsigned long)r, key, r->value);
}


/* Finds and prints the keys, pointers, and values within a range
 * of keys between key_start and key_end, including both bounds.
 */
void find_and_print_range( node * root, int key_start, int key_end,
		bool verbose ) {
	int i;
	int array_size = key_end - key_start + 1;
	int returned_keys[array_size];
	void * returned_pointers[array_size];
	int num_found = find_range( root, key_start, key_end, verbose,
			returned_keys, returned_pointers );
	if (!num_found)
		printf("None found.\n");
	else {
		for (i = 0; i < num_found; i++)
			printf("Key: %d   Location: %lx  Value: %d\n",
					returned_keys[i],
					(unsigned long)returned_pointers[i],
					((record *)
					 returned_pointers[i])->value);
	}
}


/* Finds keys and their pointers, if present, in the range specified
 * by key_start and key_end, inclusive.  Places these in the arrays
 * returned_keys and returned_pointers, and returns the number of
 * entries found.
 */
int find_range( node * root, int key_start, int key_end, bool verbose,
		int returned_keys[], void * returned_pointers[]) {
	int i, num_found;
	num_found = 0;
	node * n = find_leaf( root, key_start, verbose );
	if (n == NULL) return 0;
	for (i = 0; i < n->num_keys && n->keys[i] < key_start; i++) ;
	if (i == n->num_keys) return 0;
	while (n != NULL) {
		for ( ; i < n->num_keys && n->keys[i] <= key_end; i++) {
			returned_keys[num_found] = n->keys[i];
			returned_pointers[num_found] = n->pointers[i];
			num_found++;
		}
		n = n->pointers[order - 1];
		i = 0;
	}
	return num_found;
}


/* Traces the path from the root to a leaf, searching
 * by key.  Displays information about the path
 * if the verbose flag is set.
 * Returns the leaf containing the given key.
 */
node * find_leaf( node * root, int key, bool verbose ) {
	int i = 0;
	node * c = root;
	if (c == NULL) {
		if (verbose) 
			printf("Empty tree.\n");
		return c;
	}
	while (!c->is_leaf) {
		if (verbose) {
			printf("[");
			for (i = 0; i < c->num_keys - 1; i++)
				printf("%d ", c->keys[i]);
			printf("%d] ", c->keys[i]);
		}
		i = 0;
		while (i < c->num_keys) {
			if (key >= c->keys[i]) i++;
			else break;
		}
		if (verbose)
			printf("%d ->\n", i);
		c = (node *)c->pointers[i];
	}
	if (verbose) {
		printf("Leaf [");
		for (i = 0; i < c->num_keys - 1; i++)
			printf("%d ", c->keys[i]);
		printf("%d] ->\n", c->keys[i]);
	}
	return c;
}


/* Finds and returns the record to which
 * a key refers.
 */
record * find( node * root, int key, bool verbose ) {
	int i = 0;
	node * c = find_leaf( root, key, verbose );
	if (c == NULL) return NULL;
	for (i = 0; i < c->num_keys; i++)
		if (c->keys[i] == key) break;
	if (i == c->num_keys) 
		return NULL;
	else
		return (record *)c->pointers[i];
}

/* Finds the appropriate place to
 * split a node that is too big into two.
 */
int cut( int length ) {
	if (length % 2 == 0)
		return length/2;
	else
		return length/2 + 1;
}


// INSERTION

/* Creates a new record to hold the value
 * to which a key refers.
 */
record * make_record(int value) {
	record * new_record = (record *)malloc(sizeof(record));
	if (new_record == NULL) {
		perror("Record creation.");
		exit(EXIT_FAILURE);
	}
	else {
		new_record->value = value;
	}
	return new_record;
}


/* Creates a new general node, which can be adapted
 * to serve as either a leaf or an internal node.
 */
node * make_node( void ) {
	node * new_node;
	new_node = malloc(sizeof(node));
	if (new_node == NULL) {
		perror("Node creation.");
		exit(EXIT_FAILURE);
	}
	new_node->keys = malloc( (order - 1) * sizeof(int) );
	if (new_node->keys == NULL) {
		perror("New node keys array.");
		exit(EXIT_FAILURE);
	}
	new_node->pointers = malloc( order * sizeof(void *) );
	if (new_node->pointers == NULL) {
		perror("New node pointers array.");
		exit(EXIT_FAILURE);
	}
	new_node->is_leaf = false;
	new_node->num_keys = 0;
	new_node->parent = NULL;
	new_node->next = NULL;
	return new_node;
}

/* Creates a new leaf by creating a node
 * and then adapting it appropriately.
 */
node * make_leaf( void ) {
	node * leaf = make_node();
	leaf->is_leaf = true;
	return leaf;
}


/* Helper function used in insert_into_parent
 * to find the index of the parent's pointer to 
 * the node to the left of the key to be inserted.
 */
int get_left_index(node * parent, node * left) {

	int left_index = 0;
	while (left_index <= parent->num_keys && 
			parent->pointers[left_index] != left)
		left_index++;
	return left_index;
}

/* Inserts a new pointer to a record and its corresponding
 * key into a leaf.
 * Returns the altered leaf.
 */
node * insert_into_leaf( node * leaf, int key, record * pointer ) {

	int i, insertion_point;

	insertion_point = 0;
	while (insertion_point < leaf->num_keys && leaf->keys[insertion_point] < key)
		insertion_point++;

	for (i = leaf->num_keys; i > insertion_point; i--) {
		leaf->keys[i] = leaf->keys[i - 1];
		leaf->pointers[i] = leaf->pointers[i - 1];
	}
	leaf->keys[insertion_point] = key;
	leaf->pointers[insertion_point] = pointer;
	leaf->num_keys++;
	return leaf;
}


/* Inserts a new key and pointer
 * to a new record into a leaf so as to exceed
 * the tree's order, causing the leaf to be split
 * in half.
 */
node * insert_into_leaf_after_splitting(node * root, node * leaf, int key, record * pointer) {

	node * new_leaf;
	int * temp_keys;
	void ** temp_pointers;
	int insertion_index, split, new_key, i, j;

	new_leaf = make_leaf();

	temp_keys = malloc( order * sizeof(int) );
	if (temp_keys == NULL) {
		perror("Temporary keys array.");
		exit(EXIT_FAILURE);
	}

	temp_pointers = malloc( order * sizeof(void *) );
	if (temp_pointers == NULL) {
		perror("Temporary pointers array.");
		exit(EXIT_FAILURE);
	}

	insertion_index = 0;
	while (insertion_index < order - 1 && leaf->keys[insertion_index] < key)
		insertion_index++;

	for (i = 0, j = 0; i < leaf->num_keys; i++, j++) {
		if (j == insertion_index) j++;
		temp_keys[j] = leaf->keys[i];
		temp_pointers[j] = leaf->pointers[i];
	}

	temp_keys[insertion_index] = key;
	temp_pointers[insertion_index] = pointer;

	leaf->num_keys = 0;

	split = cut(order - 1);

	for (i = 0; i < split; i++) {
		leaf->pointers[i] = temp_pointers[i];
		leaf->keys[i] = temp_keys[i];
		leaf->num_keys++;
	}

	for (i = split, j = 0; i < order; i++, j++) {
		new_leaf->pointers[j] = temp_pointers[i];
		new_leaf->keys[j] = temp_keys[i];
		new_leaf->num_keys++;
	}

	free(temp_pointers);
	free(temp_keys);

	new_leaf->pointers[order - 1] = leaf->pointers[order - 1];
	leaf->pointers[order - 1] = new_leaf;

	for (i = leaf->num_keys; i < order - 1; i++)
		leaf->pointers[i] = NULL;
	for (i = new_leaf->num_keys; i < order - 1; i++)
		new_leaf->pointers[i] = NULL;

	new_leaf->parent = leaf->parent;
	new_key = new_leaf->keys[0];

	return insert_into_parent(root, leaf, new_key, new_leaf);
}


/* Inserts a new key and pointer to a node
 * into a node into which these can fit
 * without violating the B+ tree properties.
 */
node * insert_into_node(node * root, node * n, 
		int left_index, int key, node * right) {
	int i;

	for (i = n->num_keys; i > left_index; i--) {
		n->pointers[i + 1] = n->pointers[i];
		n->keys[i] = n->keys[i - 1];
	}
	n->pointers[left_index + 1] = right;
	n->keys[left_index] = key;
	n->num_keys++;
	return root;
}


/* Inserts a new key and pointer to a node
 * into a node, causing the node's size to exceed
 * the order, and causing the node to split into two.
 */
node * insert_into_node_after_splitting(node * root, node * old_node, int left_index, 
		int key, node * right) {

	int i, j, split, k_prime;
	node * new_node, * child;
	int * temp_keys;
	node ** temp_pointers;

	/* First create a temporary set of keys and pointers
	 * to hold everything in order, including
	 * the new key and pointer, inserted in their
	 * correct places. 
	 * Then create a new node and copy half of the 
	 * keys and pointers to the old node and
	 * the other half to the new.
	 */

	temp_pointers = malloc( (order + 1) * sizeof(node *) );
	if (temp_pointers == NULL) {
		perror("Temporary pointers array for splitting nodes.");
		exit(EXIT_FAILURE);
	}
	temp_keys = malloc( order * sizeof(int) );
	if (temp_keys == NULL) {
		perror("Temporary keys array for splitting nodes.");
		exit(EXIT_FAILURE);
	}

	for (i = 0, j = 0; i < old_node->num_keys + 1; i++, j++) {
		if (j == left_index + 1) j++;
		temp_pointers[j] = old_node->pointers[i];
	}

	for (i = 0, j = 0; i < old_node->num_keys; i++, j++) {
		if (j == left_index) j++;
		temp_keys[j] = old_node->keys[i];
	}

	temp_pointers[left_index + 1] = right;
	temp_keys[left_index] = key;

	/* Create the new node and copy
	 * half the keys and pointers to the
	 * old and half to the new.
	 */  
	split = cut(order);
	new_node = make_node();
	old_node->num_keys = 0;
	for (i = 0; i < split - 1; i++) {
		old_node->pointers[i] = temp_pointers[i];
		old_node->keys[i] = temp_keys[i];
		old_node->num_keys++;
	}
	old_node->pointers[i] = temp_pointers[i];
	k_prime = temp_keys[split - 1];
	for (++i, j = 0; i < order; i++, j++) {
		new_node->pointers[j] = temp_pointers[i];
		new_node->keys[j] = temp_keys[i];
		new_node->num_keys++;
	}
	new_node->pointers[j] = temp_pointers[i];
	free(temp_pointers);
	free(temp_keys);
	new_node->parent = old_node->parent;
	for (i = 0; i <= new_node->num_keys; i++) {
		child = new_node->pointers[i];
		child->parent = new_node;
	}

	/* Insert a new key into the parent of the two
	 * nodes resulting from the split, with
	 * the old node to the left and the new to the right.
	 */

	return insert_into_parent(root, old_node, k_prime, new_node);
}



/* Inserts a new node (leaf or internal node) into the B+ tree.
 * Returns the root of the tree after insertion.
 */
node * insert_into_parent(node * root, node * left, int key, node * right) {

	int left_index;
	node * parent;

	parent = left->parent;

	/* Case: new root. */

	if (parent == NULL)
		return insert_into_new_root(left, key, right);

	/* Case: leaf or node. (Remainder of
	 * function body.)  
	 */

	/* Find the parent's pointer to the left 
	 * node.
	 */

	left_index = get_left_index(parent, left);


	/* Simple case: the new key fits into the node. 
	 */

	if (parent->num_keys < order - 1)
		return insert_into_node(root, parent, left_index, key, right);

	/* Harder case:  split a node in order 
	 * to preserve the B+ tree properties.
	 */

	return insert_into_node_after_splitting(root, parent, left_index, key, right);
}


/* Creates a new root for two subtrees
 * and inserts the appropriate key into
 * the new root.
 */
node * insert_into_new_root(node * left, int key, node * right) {

	node * root = make_node();
	root->keys[0] = key;
	root->pointers[0] = left;
	root->pointers[1] = right;
	root->num_keys++;
	root->parent = NULL;
	left->parent = root;
	right->parent = root;
	return root;
}



/* First insertion:
 * start a new tree.
 */
node * start_new_tree(int key, record * pointer) {

	node * root = make_leaf();
	root->keys[0] = key;
	root->pointers[0] = pointer;
	root->pointers[order - 1] = NULL;
	root->parent = NULL;
	root->num_keys++;
	return root;
}



/* Master insertion function.
 * Inserts a key and an associated value into
 * the B+ tree, causing the tree to be adjusted
 * however necessary to maintain the B+ tree
 * properties.
 */
node * insert( node * root, int key, int value ) {

	record * pointer;
	node * leaf;

	/* The current implementation ignores
	 * duplicates.
	 */

	if (find(root, key, false) != NULL)
		return root;

	/* Create a new record for the
	 * value.
	 */
	pointer = make_record(value);


	/* Case: the tree does not exist yet.
	 * Start a new tree.
	 */

	if (root == NULL) 
		return start_new_tree(key, pointer);


	/* Case: the tree already exists.
	 * (Rest of function body.)
	 */

	leaf = find_leaf(root, key, false);

	/* Case: leaf has room for key and pointer.
	 */

	if (leaf->num_keys < order - 1) {
		leaf = insert_into_leaf(leaf, key, pointer);
		return root;
	}


	/* Case:  leaf must be split.
	 */

	return insert_into_leaf_after_splitting(root, leaf, key, pointer);
}




// DELETION.

/* Utility function for deletion.  Retrieves
 * the index of a node's nearest neighbor (sibling)
 * to the left if one exists.  If not (the node
 * is the leftmost child), returns -1 to signify
 * this special case.
 */
int get_neighbor_index( node * n ) {

	int i;

	/* Return the index of the key to the left
	 * of the pointer in the parent pointing
	 * to n.  
	 * If n is the leftmost child, this means
	 * return -1.
	 */
	for (i = 0; i <= n->parent->num_keys; i++)
		if (n->parent->pointers[i] == n)
			return i - 1;

	// Error state.
	printf("Search for nonexistent pointer to node in parent.\n");
	printf("Node:  %#lx\n", (unsigned long)n);
	exit(EXIT_FAILURE);
}


node * remove_entry_from_node(node * n, int key, node * pointer) {

	int i, num_pointers;

	// Remove the key and shift other keys accordingly.
	i = 0;
	while (n->keys[i] != key)
		i++;
	for (++i; i < n->num_keys; i++)
		n->keys[i - 1] = n->keys[i];

	// Remove the pointer and shift other pointers accordingly.
	// First determine number of pointers.
	num_pointers = n->is_leaf ? n->num_keys : n->num_keys + 1;
	i = 0;
	while (n->pointers[i] != pointer)
		i++;
	for (++i; i < num_pointers; i++)
		n->pointers[i - 1] = n->pointers[i];


	// One key fewer.
	n->num_keys--;

	// Set the other pointers to NULL for tidiness.
	// A leaf uses the last pointer to point to the next leaf.
	if (n->is_leaf)
		for (i = n->num_keys; i < order - 1; i++)
			n->pointers[i] = NULL;
	else
		for (i = n->num_keys + 1; i < order; i++)
			n->pointers[i] = NULL;

	return n;
}


node * adjust_root(node * root) {

	node * new_root;

	/* Case: nonempty root.
	 * Key and pointer have already been deleted,
	 * so nothing to be done.
	 */

	if (root->num_keys > 0)
		return root;

	/* Case: empty root. 
	 */

	// If it has a child, promote 
	// the first (only) child
	// as the new root.

	if (!root->is_leaf) {
		new_root = root->pointers[0];
		new_root->parent = NULL;
	}

	// If it is a leaf (has no children),
	// then the whole tree is empty.

	else
		new_root = NULL;

	free(root->keys);
	free(root->pointers);
	free(root);

	return new_root;
}


/* Coalesces a node that has become
 * too small after deletion
 * with a neighboring node that
 * can accept the additional entries
 * without exceeding the maximum.
 */
node * coalesce_nodes(node * root, node * n, node * neighbor, int neighbor_index, int k_prime) {

	int i, j, neighbor_insertion_index, n_end;
	node * tmp;

	/* Swap neighbor with node if node is on the
	 * extreme left and neighbor is to its right.
	 */

	if (neighbor_index == -1) {
		tmp = n;
		n = neighbor;
		neighbor = tmp;
	}

	/* Starting point in the neighbor for copying
	 * keys and pointers from n.
	 * Recall that n and neighbor have swapped places
	 * in the special case of n being a leftmost child.
	 */

	neighbor_insertion_index = neighbor->num_keys;

	/* Case:  nonleaf node.
	 * Append k_prime and the following pointer.
	 * Append all pointers and keys from the neighbor.
	 */

	if (!n->is_leaf) {

		/* Append k_prime.
		 */

		neighbor->keys[neighbor_insertion_index] = k_prime;
		neighbor->num_keys++;


		n_end = n->num_keys;

		for (i = neighbor_insertion_index + 1, j = 0; j < n_end; i++, j++) {
			neighbor->keys[i] = n->keys[j];
			neighbor->pointers[i] = n->pointers[j];
			neighbor->num_keys++;
			n->num_keys--;
		}

		/* The number of pointers is always
		 * one more than the number of keys.
		 */

		neighbor->pointers[i] = n->pointers[j];

		/* All children must now point up to the same parent.
		 */

		for (i = 0; i < neighbor->num_keys + 1; i++) {
			tmp = (node *)neighbor->pointers[i];
			tmp->parent = neighbor;
		}
	}

	/* In a leaf, append the keys and pointers of
	 * n to the neighbor.
	 * Set the neighbor's last pointer to point to
	 * what had been n's right neighbor.
	 */

	else {
		for (i = neighbor_insertion_index, j = 0; j < n->num_keys; i++, j++) {
			neighbor->keys[i] = n->keys[j];
			neighbor->pointers[i] = n->pointers[j];
			neighbor->num_keys++;
		}
		neighbor->pointers[order - 1] = n->pointers[order - 1];
	}

	root = delete_entry(root, n->parent, k_prime, n);
	free(n->keys);
	free(n->pointers);
	free(n); 
	return root;
}


/* Redistributes entries between two nodes when
 * one has become too small after deletion
 * but its neighbor is too big to append the
 * small node's entries without exceeding the
 * maximum
 */
node * redistribute_nodes(node * root, node * n, node * neighbor, int neighbor_index, 
		int k_prime_index, int k_prime) {  

	int i;
	node * tmp;

	/* Case: n has a neighbor to the left. 
	 * Pull the neighbor's last key-pointer pair over
	 * from the neighbor's right end to n's left end.
	 */

	if (neighbor_index != -1) {
		if (!n->is_leaf)
			n->pointers[n->num_keys + 1] = n->pointers[n->num_keys];
		for (i = n->num_keys; i > 0; i--) {
			n->keys[i] = n->keys[i - 1];
			n->pointers[i] = n->pointers[i - 1];
		}
		if (!n->is_leaf) {
			n->pointers[0] = neighbor->pointers[neighbor->num_keys];
			tmp = (node *)n->pointers[0];
			tmp->parent = n;
			neighbor->pointers[neighbor->num_keys] = NULL;
			n->keys[0] = k_prime;
			n->parent->keys[k_prime_index] = neighbor->keys[neighbor->num_keys - 1];
		}
		else {
			n->pointers[0] = neighbor->pointers[neighbor->num_keys - 1];
			neighbor->pointers[neighbor->num_keys - 1] = NULL;
			n->keys[0] = neighbor->keys[neighbor->num_keys - 1];
			n->parent->keys[k_prime_index] = n->keys[0];
		}
	}

	/* Case: n is the leftmost child.
	 * Take a key-pointer pair from the neighbor to the right.
	 * Move the neighbor's leftmost key-pointer pair
	 * to n's rightmost position.
	 */

	else {  
		if (n->is_leaf) {
			n->keys[n->num_keys] = neighbor->keys[0];
			n->pointers[n->num_keys] = neighbor->pointers[0];
			n->parent->keys[k_prime_index] = neighbor->keys[1];
		}
		else {
			n->keys[n->num_keys] = k_prime;
			n->pointers[n->num_keys + 1] = neighbor->pointers[0];
			tmp = (node *)n->pointers[n->num_keys + 1];
			tmp->parent = n;
			n->parent->keys[k_prime_index] = neighbor->keys[0];
		}
		for (i = 0; i < neighbor->num_keys - 1; i++) {
			neighbor->keys[i] = neighbor->keys[i + 1];
			neighbor->pointers[i] = neighbor->pointers[i + 1];
		}
		if (!n->is_leaf)
			neighbor->pointers[i] = neighbor->pointers[i + 1];
	}

	/* n now has one more key and one more pointer;
	 * the neighbor has one fewer of each.
	 */

	n->num_keys++;
	neighbor->num_keys--;

	return root;
}


/* Deletes an entry from the B+ tree.
 * Removes the record and its key and pointer
 * from the leaf, and then makes all appropriate
 * changes to preserve the B+ tree properties.
 */
node * delete_entry( node * root, node * n, int key, void * pointer ) {

	int min_keys;
	node * neighbor;
	int neighbor_index;
	int k_prime_index, k_prime;
	int capacity;

	// Remove key and pointer from node.

	n = remove_entry_from_node(n, key, pointer);

	/* Case:  deletion from the root. 
	 */

	if (n == root) 
		return adjust_root(root);


	/* Case:  deletion from a node below the root.
	 * (Rest of function body.)
	 */

	/* Determine minimum allowable size of node,
	 * to be preserved after deletion.
	 */

	min_keys = n->is_leaf ? cut(order - 1) : cut(order) - 1;

	/* Case:  node stays at or above minimum.
	 * (The simple case.)
	 */

	if (n->num_keys >= min_keys)
		return root;

	/* Case:  node falls below minimum.
	 * Either coalescence or redistribution
	 * is needed.
	 */

	/* Find the appropriate neighbor node with which
	 * to coalesce.
	 * Also find the key (k_prime) in the parent
	 * between the pointer to node n and the pointer
	 * to the neighbor.
	 */

	neighbor_index = get_neighbor_index( n );
	k_prime_index = neighbor_index == -1 ? 0 : neighbor_index;
	k_prime = n->parent->keys[k_prime_index];
	neighbor = neighbor_index == -1 ? n->parent->pointers[1] : 
		n->parent->pointers[neighbor_index];

	capacity = n->is_leaf ? order : order - 1;

	/* Coalescence. */

	if (neighbor->num_keys + n->num_keys < capacity)
		return coalesce_nodes(root, n, neighbor, neighbor_index, k_prime);

	/* Redistribution. */

	else
		return redistribute_nodes(root, n, neighbor, neighbor_index, k_prime_index, k_prime);
}



/* Master deletion function.
 */
node * delete(node * root, int key) {

	node * key_leaf;
	record * key_record;

	key_record = find(root, key, false);
	key_leaf = find_leaf(root, key, false);
	if (key_record != NULL && key_leaf != NULL) {
		root = delete_entry(root, key_leaf, key, key_record);
		free(key_record);
	}
	return root;
}


void destroy_tree_nodes(node * root) {
	int i;
	if (root->is_leaf)
		for (i = 0; i < root->num_keys; i++)
			free(root->pointers[i]);
	else
		for (i = 0; i < root->num_keys + 1; i++)
			destroy_tree_nodes(root->pointers[i]);
	free(root->pointers);
	free(root->keys);
	free(root);
}


node * destroy_tree(node * root) {
	destroy_tree_nodes(root);
	return NULL;
}


// MAIN

int main( int argc, char ** argv ) {

	char * input_file;
	FILE * fp;
	node * root;
	int input, range2;
	char instruction;
	char license_part;

	root = NULL;
	verbose_output = false;

	if (argc > 1) {
		order = atoi(argv[1]);
		if (order < MIN_ORDER || order > MAX_ORDER) {
			fprintf(stderr, "Invalid order: %d .\n\n", order);
			usage_3();
			exit(EXIT_FAILURE);
		}
	}

	license_notice();
	usage_1();  
	usage_2();

	if (argc > 2) {
		input_file = argv[2];
		fp = fopen(input_file, "r");
		if (fp == NULL) {
			perror("Failure to open input file.");
			exit(EXIT_FAILURE);
		}
		while (!feof(fp)) {
			fscanf(fp, "%d\n", &input);
			root = insert(root, input, input);
		}
		fclose(fp);
		print_tree(root);
	}

	printf("> ");
	while (scanf("%c", &instruction) != EOF) {
		switch (instruction) {
		case 'd':
			scanf("%d", &input);
			root = delete(root, input);
			print_tree(root);
			break;
		case 'i':
			scanf("%d", &input);
			root = insert(root, input, input);
			print_tree(root);
			break;
		case 'f':
		case 'p':
			scanf("%d", &input);
			find_and_print(root, input, instruction == 'p');
			break;
		case 'r':
			scanf("%d %d", &input, &range2);
			if (input > range2) {
				int tmp = range2;
				range2 = input;
				input = tmp;
			}
			find_and_print_range(root, input, range2, instruction == 'p');
			break;
		case 'l':
			print_leaves(root);
			break;
		case 'q':
			while (getchar() != (int)'\n');
			return EXIT_SUCCESS;
		case 's':
			if (scanf("how %c", &license_part) == 0) {
				usage_2();
				break;
			}
			switch(license_part) {
			case 'w':
				print_license(LICENSE_WARRANTEE);
				break;
			case 'c':
				print_license(LICENSE_CONDITIONS);
				break;
			default:
				usage_2();
				break;
			}
			break;
		case 't':
			print_tree(root);
			break;
		case 'v':
			verbose_output = !verbose_output;
			break;
		case 'x':
			if (root)
				root = destroy_tree(root);
			print_tree(root);
			break;
		default:
			usage_2();
			break;
		}
		while (getchar() != (int)'\n');
		printf("> ");
	}
	printf("\n");

	return EXIT_SUCCESS;
}