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

// 定義基本的資料結構和型別預定義
struct TreeNode;
typedef struct TreeNode *Position;
typedef struct TreeNode *SearchTree;
typedef int ElementType;

struct TreeNode
{
    ElementType Element;
    SearchTree Left;
    SearchTree Right;
};

// 二叉樹遞迴插入元素
SearchTree Insert(ElementType X, SearchTree T
 
)
{
    if (T == NULL)
    {
        T = (SearchTree)malloc(sizeof(struct TreeNode));
        if (T == NULL)
        {
            printf("tree malloc failed.\n");
            return NULL;
        }
        T->Element = X;
        T->Left = T->Right = NULL;
    }
    else if (X < T->Element)
    {
        T
 
->Left = Insert(X, T->Left);
    }
    else if (X > T->Element)
    {
        T->Right = Insert(X, T->Right);
    }
    return T;
}

// 遞迴的查詢某個元素
SearchTree Find(ElementType X, SearchTree T)
{
    if (T == NULL)
    {
        return NULL;
    }
    else if (X < T->Element)
    {
        return
 
 Find(X, T->Left);
    }
    else if (X > T->Element)
    {
        return Find(X, T->Right);
    }
    else
    {
        return T;
    }
}

// 遞迴的前序遍歷
ElementType PreOrder(SearchTree T)
{
    if (T != NULL)
    {
        printf("%d\n", T->Element);
        PreOrder(T->Left);
        PreOrder(T->Right);
    }
}

// 遞迴的查詢最小的元素所在的指標
SearchTree FindMin(SearchTree T)
{
    if (T == NULL)
    {
        return NULL;
    }
    else if (T->Left == NULL)
    {
        return T;
    }
    else
    {
        return FindMin(T->Left);
    }
}

// 遞迴的刪除某個元素
SearchTree Delete(ElementType X, SearchTree T)
{
    Position TmpCell;

    if (T == NULL)
    {
        printf("element not fount!\n");
    }
    else if (X < T->Element)
    {
        T->Left = Delete(X, T->Left);
    }
    else if (X > T->Element)
    {
        T->Right = Delete(X, T->Right);
    }
    else if (T->Left && T->Right)
    {
        // 處理待刪除節點有兩個子節點情況，採取將右子樹的最小節點代替刪除的節點，也可以使用
        // 左子樹的最大節點代替刪除的元素
        TmpCell = FindMin(T->Right);
        T->Element = TmpCell->Element;
        T->Right = Delete(T->Element, T->Right);
    }
    else
    {
        // 處理節點只有一個子節點或沒有子節點的情況
        TmpCell = T;
        if (T->Left == NULL)
            T = T->Right;
        else if (T->Right == NULL)
            T = T->Left;
        free(TmpCell);
    }
    return T;
}

int main()
{
    //一定初始化T為NULL，否則後續插入判斷根節點是否為NULL會出錯
    SearchTree T = NULL;
    T = Insert(2, T);
    T = Insert(1, T);
    T = Insert(3, T);
    PreOrder(T);
    Delete(1, T);
    PreOrder(T);
    // Position tmp = FindMin(T);
    // printf("%d\n", tmp->Element);
    return 0;
}