技術標籤：PTA佇列二叉樹資料結構

6-6Level-order Traversal(25point(s))

Write a routine to list out the nodes of a binary tree in "level-order". List the root, then nodes at depth 1, followed by nodes at depth 2, and so on. You must do this in linear time.

Format of functions:

void Level_order ( Tree T, void (*visit)(Tree ThisNode) );
 

wherevoid (*visit)(Tree ThisNode)is a function that handlesThisNodebeing visited byLevel_order, andTreeis defined as the following:

typedef struct TreeNode *Tree;
struct TreeNode {
    ElementType Element;
    Tree  Left;
    Tree  Right;
};

Sample program of judge:

#include <stdio.h>
#include <stdlib.h>

#define MaxTree 10 /* maximum number of nodes in a tree */
typedef int ElementType;

typedef struct TreeNode *Tree;
struct TreeNode {
    ElementType Element;
    Tree  Left;
    Tree  Right;
};

Tree BuildTree(); /* details omitted */
void PrintNode( Tree NodePtr )
{
   printf(" %d", NodePtr->Element);
}

void Level_order ( Tree T, void (*visit)(Tree ThisNode) );

int main()
{
    Tree T = BuildTree();
    printf("Level-order:");
    Level_order(T, PrintNode);
    return 0;
}

/* Your function will be put here */
 

Sample Output (for the tree shown in the figure):

Level-order: 3 5 6 1 8 10 9

Example:

void Level_order ( Tree T, void (*visit)(Tree ThisNode) )
{
    Tree Q[MaxTree];
    int front = 0, rear = 0;
    if(T) Q[rear++] = T;
    while(front < rear) {
        T = Q[front++];
        visit(T);
        if(T->Left)  Q[rear++] = T->Left;
        if(T->Right) Q[rear++] = T->Right;
    }
}
 

思路：

層次遍歷，從隊列出隊一個結點，visit，然後將左孩子，右孩子依次進隊，直至佇列為空.