98. 验证二叉搜索树C++

/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class Solution { public: bool isValidBST(TreeNode* root) { if(!root) return true; stack<TreeNode*> stack; TreeNode* cur = root; long value = LONG_MIN; while(cur || !stack.empty()){ while(cur){ stack.push(cur); cur=cur->left; } cur = stack.top(); stack.pop(); if(cur->val<=value) return false; value = cur->val; cur=cur->right; } return true; } };