Leetcode 98 Validate Binary Search Tree

triplebee

发布于 2018-01-12 14:55:00

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文章被收录于专栏：计算机视觉与深度学习基础计算机视觉与深度学习基础

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.

判断二叉搜索树是否合法。

DFS，记录上下界，在每个点判断值是否满足上下界，然后再继续向下访问。

/**
 * 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 dfs(TreeNode* root,long long minn,long long maxx)
    {
        if(!root) return true;
        if(root->val<=minn || root->val>=maxx) return false;
        if(dfs(root->left,minn,root->val) && dfs(root->right,root->val,maxx)) return true;
        return false;
    }
    bool isValidBST(TreeNode* root) {
        return dfs(root,(long long)INT_MIN-1,(long long)INT_MAX+1);
    }
};

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原始发表：2016-10-08 ，如有侵权请联系 cloudcommunity@tencent.com 删除

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Leetcode 98 Validate Binary Search Tree

Leetcode 98 Validate Binary Search Tree

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