leetcode/algorithms/cpp/longestUnivaluePath/longestUnivaluePath.cpp at main · MichelleZ/leetcode · GitHub

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// Source: https://leetcode.com/problems/longest-univalue-path/
// Author: Miao Zhang
// Date:   2021-03-01

/**
 * 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 longestUnivaluePath(TreeNode* root) {
        if (!root) return 0;
        int res = 0;
        univaluePath(root, res);
        return res;
    }

private:
    int univaluePath(TreeNode* root, int& res) {
        if (!root) return 0;
        int l = univaluePath(root->left, res);
        int r = univaluePath(root->right, res);
        int pl = 0;
        int pr = 0;
        if (root->left && root->val == root->left->val) pl = l + 1;
        if (root->right && root->val == root->right->val) pr = r + 1;
        res = max(res, pl + pr);
        return max(pl, pr);
    }
};