965. Univalued Binary Tree -------E

Q:

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].

A:

/**
 * 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:
    bool isUnivalTree(TreeNode* root) {
        if(!root)
            return true;
        return helper(root,root->val);
    }
private:
    bool helper(TreeNode * root, const int val){
        if(!root)
            return true;
        if(root->val != val)
            return false;
        if( ! helper(root->left, val))
            return false;
        return helper(root->right, val);
    }
};