用c语言试写一个判别给定二叉树是否为二叉排序树的程序

以下是用C语言实现的判断二叉树是否为二叉排序树的程序：

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

typedef struct TreeNode {
    int val;
    struct TreeNode* left;
    struct TreeNode* right;
} TreeNode;

bool isValidBSTHelper(TreeNode* root, int* lower, int* upper) {
    if (root == NULL) {
        return true;
    }
    if (lower != NULL && root->val <= *lower) {
        return false;
    }
    if (upper != NULL && root->val >= *upper) {
        return false;
    }
    return isValidBSTHelper(root->left, lower, &root->val) &&
           isValidBSTHelper(root->right, &root->val, upper);
}

bool isValidBST(TreeNode* root) {
    return isValidBSTHelper(root, NULL, NULL);
}

int main() {
    // 构造一个二叉排序树
    TreeNode* root = (TreeNode*)malloc(sizeof(TreeNode));
    root->val = 5;
    root->left = (TreeNode*)malloc(sizeof(TreeNode));
    root->left->val = 3;
    root->left->left = (TreeNode*)malloc(sizeof(TreeNode));
    root->left->left->val = 1;
    root->left->left->left = NULL;
    root->left->left->right = NULL;
    root->left->right = (TreeNode*)malloc(sizeof(TreeNode));
    root->left->right->val = 4;
    root->left->right->left = NULL;
    root->left->right->right = NULL;
    root->right = (TreeNode*)malloc(sizeof(TreeNode));
    root->right->val = 7;
    root->right->left = (TreeNode*)malloc(sizeof(TreeNode));
    root->right->left->val = 6;
    root->right->left->left = NULL;
    root->right->left->right = NULL;
    root->right->right = (TreeNode*)malloc(sizeof(TreeNode));
    root->right->right->val = 8;
    root->right->right->left = NULL;
    root->right->right->right = NULL;

    printf("输入的二叉树%s是二叉排序树\n", isValidBST(root) ? "" : "不");
    return 0;
}

程序中使用了递归的方法，isValidBSTHelper函数用于判断以root为根的子树是否为二叉排序树，lower和upper参数分别表示root的值应该在的区间。isValidBST函数则调用了isValidBSTHelper函数，将lower和upper都初始化为NULL，表示不限制。最后在main函数中构造了一个二叉排序树，并输出是否为二叉排序树的结果。