Univalued Binary Tree

Box

2020-06-02

965. Univalued Binary Tree

Question:

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:

Using dfs to traverse the node and find the difference.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    int target;
    public boolean isUnivalTree(TreeNode root) {
       target = root.val;  
       return dfs(root);
    }
    public boolean dfs(TreeNode root){
        if (root == null) return true;
        if (root.val == target) {
           return dfs(root.left) && dfs(root.right);
        } else {
           return false;
        }
    }
}