LeetCode:Validate Binary Search Tree

Given a binary tree, determine if it is a valid binary search tree (BST).

Assume a BST is defined as follows:

The left subtree of a node contains only nodes with keys less than the node’s key.

The right subtree of a node contains only nodes with keys greater than the node’s key.

Both the left and right subtrees must also be binary search trees.

Example 1:
2
/ \
1   3
Binary tree [2,1,3], return true.

Example 2:
1
/ \
2   3
Binary tree [1,2,3], return false.

Solution:

递归解决比较简单粗暴

考虑条件：

1. 终止条件
2. BST条件

#include "iostream"

using namespace std;

struct TreeNode*{
int val;
TreeNode* left;
TreeNode* right;
TreeNode(int x):val(x),left(NULL),right(NULL){};
};

class Solution{
public:
bool isValidBST(TreeNode* root){
return support(root,LONG_MIN,LONG_MAX);
}
bool support(TreeNode* root,long min,long max);
};

bool Solution::support(TreeNode* root,long min,long max)
{
if(root==NULL)
return true;
if(root->val<=min||root->val>=max)
return false;
return support(root->left,min,root->val)&&support(root->right,root->val,max);
}
int main()
{
return 0;
}