Leetcode 965. Univalued Binary Tree

Posted 2022-11-30 逆風的薔薇

题目

A binary tree is univalued if every node in the tree has the same value.

Return true if and only if the given tree is univalued.

 

Example 1:

Input: [1,1,1,1,1,null,1]
Output: true

Example 2:

Input: [2,2,2,5,2]
Output: false

Note:

1. The number of nodes in the given tree will be in the range [1, 100].
2. Each node's value will be an integer in the range [0, 99].

分析

1. 遍历，验证数组

2. 递归

代码

/**
 * Definition for a binary tree node.
 * public class TreeNode 
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x)  val = x; 
 * 
 */
class Solution 
    /*public boolean isUnivalTree(TreeNode root) 
        if (root == null) 
            return true;
        
        
        if (root.left != null && root.val != root.left.val) 
            return false;
        

        if (root.right != null && root.val != root.right.val) 
            return false;
        

        return isUnivalTree(root.left) && isUnivalTree(root.right);
    */
    
    public boolean isUnivalTree(TreeNode root) 
        if (root == null) 
            return true;
        
        
        boolean leftRet = root.left == null || (root.val == root.left.val && isUnivalTree(root.left));
        
        boolean rightRet = root.right == null || (root.val == root.right.val && isUnivalTree(root.right));

        return leftRet && rightRet;