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:

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].

Difficulty:Easy

Category:Tree

Analyze

Solution

class Solution {
 public:
  bool isUnivalTree(TreeNode* root) {
    if (!root) return true;
    int val = root->val;
    return isUnivalTree(root, val);
  }
  bool isUnivalTree(TreeNode* root, int val) {
    if (!root) return true;
    if (root->val == val) {
      return isUnivalTree(root->left, val) && isUnivalTree(root->right, val);
    } else {
      return false;
    }
  }
};