c_cpp validat_bst.cpp

Posted 2021-05-14

/**
 * 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) {

    //travel the tree by inner-order
    vector<TreeNode*> stack;
    TreeNode* node = root;
    vector<int> v;
    while (stack.size()>0 || node!=NULL) {
        if (node!=NULL){
            stack.push_back(node);
            node = node->left;
        }else{
            node = stack.back();
            stack.pop_back();
            v.push_back(node->val);
            node = node->right;
        }
    }

    //check the vector wehther sorted or not
    for(int i=0; v.size()>0 && i<v.size()-1; i++){
        if (v[i] >= v[i+1]) {
            return false;
        }
    }

    return true;
}

};