250. (Locked)Count Univalue Subtrees

Difficulty: Medium

Frequency: N/A

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.


My solution:
Data structure:
Steps:
Complexity:
Runtime:
Space:
Test cases:
Corner cases:
Code:
/**
 * 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 cnt = 0;
        countSubtree(root, cnt);
        return cnt;
    }
    bool countSubtree(TreeNode* node, int& cnt) {
        if (!node) return false;
        if (!node->left && !node->right) {
            cnt++;
            return true;
        }
        bool left = countSubtree(node->left, cnt);
        bool right = countSubtree(node->right, cnt);
        if (left && right && (!node->left || node->left->val == node->val) && (!node->right || node->right->val == node->val)) {
            cnt++;
            return true;
        }
        return false;
    }
}

Another solution:
Data structure:
steps:
Complexity:
Runtime:
Space:
Code:

Things to learn:
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