注意root指针需要事先判别是否是NULL

965. Univalued Binary Tree

Easy

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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

/**
 * 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) {
        if(root == NULL){
            return false;
        }
        Value = root->val;
        return isTree(root);
    }
    bool isTree(TreeNode* root){
        if(root == NULL){return  true;}
        if(root->val != Value){
            return false;
        }
        return isTree(root->left) && isTree(root->right);
    }
private:
    int Value;
};