[leetcode]Validate Binary Search Tree

左子树的任意节点的值都比root小

右子树的任意节点的值都比root大

 

TAT怎么做。。。

递归的时候设置个上下界就好了。。。

左子树，更新上届

右子树，更新下界

 

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool valid(TreeNode* root , int lower , int upper){
        if (root == nullptr) return true;
        return root -> val > lower && root -> val < upper && valid(root -> left , lower , root -> val) && valid(root -> right , root -> val , upper); 
    }
    bool isValidBST(TreeNode *root) {
        return valid(root , INT_MIN , INT_MAX);
    }
};

 

-------2014/12/18------

没考虑root->val是INT_MAX或者INT_MIN的情况

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool v(TreeNode* root, long long minv, long long maxv) {
        if (root == nullptr) return true;
        if (root->val > minv && root->val < maxv) {
            return v(root->left, minv, root->val)
                   && v(root->right, root->val, maxv);
        } else {
            return false;
        }
    }
    bool isValidBST(TreeNode *root) {
        return v(root, (long long)INT_MIN - 1, (long long)INT_MAX + 1);
    }
};