Leetcode 687 Solution

This article provides solution to leetcode question 687 (longest-univalue-path)
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https://leetcode.com/problems/longest-univalue-path

Solution

/**
 * 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 {
    int ans;
public:
    int _longestUnivalueDepth(TreeNode* root) {
        if (!root)
            return 0;

        int left_depth = root->left ? _longestUnivalueDepth(root->left) : 0;
        int right_depth = root->right ? _longestUnivalueDepth(root->right) : 0;

        int path = 0;
        int depth = 0;
        if (root->left && root->val == root->left->val)
        {
            path += left_depth + 1;
            depth = max(depth, left_depth + 1);
        }
        if (root->right && root->val == root->right->val)
        {
            path += right_depth + 1;
            depth = max(depth, right_depth + 1);
        }

        ans = max(ans, path);
        return depth;
    }

    int longestUnivaluePath(TreeNode* root) {
        ans = 0;
        _longestUnivalueDepth(root);
        return ans;
    }
};