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:
![](https://assets.leetcode.com/uploads/2018/12/28/unival_bst_2.png)
Input: [2,2,2,5,2]
Output: false
反正就是尽量用traverse。少用bst的模板(哪怕是bst),因为没人用
class Solution {
int val = -1;
public boolean isUnivalTree(TreeNode root) {
if (root == null) return true;
if (val < 0) val = root.val;
return root.val == val && isUnivalTree(root.left) && isUnivalTree(root.right);
}
}