[每日 LeetCode] 965. Univalued Binary Tree

原文链接 [每日 LeetCode] 965. Univalued Binary Tree

Description:

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

思路：本题要求判断二叉树中每个结点的值是否相同，直接遍历即可，这里使用 DFS。

C++ 代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isUnivalTree(TreeNode* root) {
        return dfs(root->left, root->val) && dfs(root->right, root->val);
    }
    bool dfs(TreeNode* root, int value){
        if (!root)
            return true;
        if (root->val != value)
            return false;
        return dfs(root->left, value) && dfs(root->right, value);
    }
};

运行时间：4ms

运行内存：10.8M