文章目录
一、题目
A binary tree is uni-valued if every node in the tree has the same value.
Given the root of a binary tree, return true if the given tree is uni-valued, or false otherwise.
Example 1:
Input: root = 1,1,1,1,1,null,1
Output: true
Example 2:
Input: root = 2,2,2,5,2
Output: false
Constraints:
The number of nodes in the tree is in the range 1, 100.
0 <= Node.val < 100
二、题解
cpp
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
TreeNode* pre;
bool isUnivalTree(TreeNode* root) {
if(root == nullptr) return true;
if(pre != nullptr){
if(pre->val != root->val) return false;
}
pre = root;
bool leftUni = isUnivalTree(root->left);
bool rightUni = isUnivalTree(root->right);
return leftUni && rightUni;
}
};