# Leetcode 250. Count Univalue Subtrees (Medium) (cpp)

2016-12-26

Leetcode 250 Count Univalue Subtrees (Medium) (cpp)

Leetcode 250. Count Univalue Subtrees (Medium) (cpp)

Tag: Tree

Difficulty: Medium

```/*

250. Count Univalue Subtrees (Medium)

Given a binary tree, count the number of uni-value subtrees.

A Uni-value subtree means all nodes of the subtree have the same value.

For example:
Given binary tree,
5
/ \
1   5
/ \   \
5   5   5
return 4.

*/
/**
* 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:
int countUnivalSubtrees(TreeNode* root) {
int res = 0;
cout(root, res);
return res;
}
private:
int cout(TreeNode* root, int& res) {
if (root == NULL) {
return 0;
}
else if (root->left == NULL && root->right == NULL) {
res++;
return 1;
}
int l = cout(root->left, res), r = cout(root->right, res);
if (l == 1 && r == 1) {
if (root->val == root->left->val && root->val == root->right->val) {
res += 1;
return 1;
}
}
else if (l == -1 || r == -1) {
return -1;
}
else if (l != 0 && root->val == root->left->val) {
res += 1;
return 1;
}
else if (r != 0 && root->val == root->right->val) {
res += 1;
return 1;
}
return -1;
}
};```