# Leetcode 965. Univalued Binary Tree (0ms)
###### tags: `Leetcode`

題目
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

解法:
1.分五種情況
a.root == NULL
b.左右子節點都是NULL
c.左節點是NULL、右節點不是NULL
d.把c.相反
e.左右都不是NULL

＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */


bool isUnivalTree(struct TreeNode* root){
    if(root == NULL)
        return true;
    if(root->left == NULL && root->right == NULL)
        return true;
    if(root->left != NULL && root->right == NULL)
    {
        if(root->left->val == root->val)
            return isUnivalTree(root->left);
        else
            return false;
    }
    
    if(root->right != NULL && root->left == NULL)
    {
        if(root->right->val == root->val)
            return isUnivalTree(root->right);
        else
            return false;
    }
    if(root->val == root->left->val && root->val == root->right->val)
        return isUnivalTree(root->left) & isUnivalTree(root->right);
    else
        return false;
    
}