965. Univalued Binary Tree - Easy

发布时间：2020-12-14 05:17:46 所属栏目：大数据来源：网络整理

导读：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,null,1]Output: true Example 2: Input: [2,2,5,2]Output: false ? Note: The number o

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,null,1]
Output: true

Example 2:

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

Note:

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

recursion

time: O(n),space: O(height)

/**
 * 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.right == 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);
    }
}

（编辑：李大同）

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