250. Count Univalue Subtrees

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250. Count Univalue Subtrees

Description

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

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

Example 1:

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Input: root = [5,1,5,5,5,null,5]
Output: 4

Example 2:

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Input: root = []
Output: 0

Example 3:

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Input: root = [5,5,5,5,5,null,5]
Output: 6

Constraints:

  • The number of the node in the tree will be in the range [0, 1000].
  • -1000 <= Node.val <= 1000

Hints/Notes

  • N/A

Solution

Language: C++

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/**
 * 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:
    int res = 0;

    int countUnivalSubtrees(TreeNode* root) {
        traverse(root);
        return res;
    }

    int traverse(TreeNode* root) {
        if (!root) {
            return INT_MIN;
        }

        int left = root->left ? traverse(root->left) : root->val;
        int right = root->right ? traverse(root->right) : root->val;

        if (left == root->val && right == root->val) {
            res++;
            return root->val;
        } else {
            return INT_MIN;
        }
    }
};