题解 | #判断是不是二叉搜索树#

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 * };
 */
/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 * 
 * @param root TreeNode类 
 * @return bool布尔型
 */
 #include <limits.h>
int front=INT_MIN;
bool judge = true;
 void is_bst(struct TreeNode* root){
    if(root==NULL)return ;
    is_bst(root->left);
    if(front>root->val) judge = false;
    front = root->val; 
    is_bst(root->right);
 }
bool isValidBST(struct TreeNode* root ) {
    // write code here
    is_bst(root);
    return judge;
}