LeetCode: Validata Binary Search Tree
Given a binary tree, determine if it is a valid binary search tree (BST).
Assume a BST is defined as follows:
地址：https://oj.leetcode.com/problems/validate-binary-search-tree/
算法：中序遍历，看看遍历到的节点值是否递增。代码：
1 /**
2 * Definition for binary tree
3 * struct TreeNode {
4 * int val;
5 * TreeNode *left;
6 * TreeNode *right;
7 * TreeNode(int x) : val(x), left(NULL), right(NULL) {}
8 * };
9 */
10 class Solution {
11 public:
12 bool isValidBST(TreeNode *root) {
13 if(!root) return true;
14 stack<TreeNode*> stk;
15 TreeNode *p = root;
16 while(p){
17 stk.push(p);
18 p = p->left;
19 }
20 TreeNode *pre = NULL;
21 p = NULL;
22 while(!stk.empty()){
23 pre = p;
24 p = stk.top();
25 stk.pop();
26 if(pre && p->val <= pre->val){
27 return false;
28 }
29 if(p->right){
30 TreeNode *q = p->right;
31 while(q){
32 stk.push(q);
33 q = q->left;
34 }
35 }
36 }
37 return true;
38 }
39 };
LeetCode: Validata Binary Search Tree
原文：http://www.cnblogs.com/boostable/p/leetcode_validate_binary_search_tree.html