leetcode 98 Validate Binary Search Tree ----- java

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.

判断一棵树是否是二叉搜索树。

判定范围即可。主要出问题的是出现在int的最大值,最小值附近。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

public class Solution {
    int flag1 = 0;
    int flag2 = 0;
    public boolean isValidBST(TreeNode root) {
           return isBST(root,Integer.MAX_VALUE,Integer.MIN_VALUE);
    }
    public boolean isBST(TreeNode root,int max,int min){
        if( root == null )
            return true;
        if( root.val == Integer.MAX_VALUE && max == root.val ){
            if( flag1 == 0){
                flag1 = 1;
                return isBST(root.right,max,root.val) && isBST(root.left,root.val,min);
            }
            else
                return false;
        }
        if( root.val == Integer.MIN_VALUE && min == root.val ){
            if( flag2 == 0){
                flag2 = 1;
                return isBST(root.right,max,root.val) && isBST(root.left,root.val,min);
            }
            else
                return false;
        }
        if( root.val <=min || root.val >= max)
            return false;
        return isBST(root.right,max,root.val) && isBST(root.left,root.val,min);

    }
}

所以可以稍微优化一下。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

public class Solution {
    public boolean isValidBST(TreeNode root) {
        return dfs(root, (long)(Integer.MIN_VALUE)-1, (long)(Integer.MAX_VALUE)+1);
    }
    private boolean dfs(TreeNode root, long gt, long lt){
        if(root == null) return true;
        if(root.val >= lt || root.val <= gt) return false;
        return dfs(root.left, gt, root.val) && dfs(root.right, root.val, lt);
    }

}
时间: 2024-10-12 14:32:45

leetcode 98 Validate Binary Search Tree ----- java的相关文章

[Lintcode]95. Validate Binary Search Tree/[Leetcode]98. Validate Binary Search Tree

95. Validate Binary Search Tree/98. Validate Binary Search Tree 本题难度: Easy Topic: Binary Tree Description 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 contain

[leetcode]98. Validate Binary Search Tree验证BST

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

LeetCode 98 Validate Binary Search Tree判断是否为合法二叉树

1 /** 2 * Definition for a binary tree node. 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 Left(TreeNode* left,

【LeetCode】Validate Binary Search Tree

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

LeetCode OJ - Validate Binary Search Tree

题目: 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

[Leetcode][BST][Validate Binary Search Tree]

判断一颗树是不是二分查找树,非常经典基础的一个算法. 我很久之前第一次做的时候,是先求出来了树的前序遍历的结果,然后判断这个数组排序后是否和排序前相同,还要判断重复虾米的,很纠结的一种做法. 后来思考了一下怎么用递归的思路做,觉得应该根据定义返回两个子树的最大值和最小值,写了一会代码,发现好麻烦,不太对的样子. 后来看了题解,发现是用了一种反向的思维,把上下界从树的顶端传下去,而不是自下而上的约束.作者太机智了. 1 /** 2 * Definition for binary tree 3 *

[LeetCode 题解]: Validate Binary Search Tree

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

leetcode dfs Validate Binary Search Tree

Validate Binary Search Tree Total Accepted: 23828 Total Submissions: 91943My Submissions 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

leetcode 之 Validate Binary Search Tree

Validate Binary Search Tree 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 c