965. Univalued Binary Tree.md

965. Univalued Binary Tree

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:

• 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].

Solution

• java
  • mine Runtime: 0 ms, faster than 100.00% of Java online submissions

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    class Solution {
        int val = -1;
        public boolean isUnivalTree(TreeNode root) {
            if(root == null){
                return true;
            }
            if(val == -1){
                val = root.val;
            }
            if(val != root.val){
                return false;
            }
            if(root.left == null && root.right == null){
                return true;
            }
            return isUnivalTree(root.left) && isUnivalTree(root.right);
        }
    }