[leetcode]687. Longest Univalue Path

[leetcode]687. Longest Univalue Path

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Analysis

ummmm~—— [ummmm~]

Given a binary tree, find the length of the longest path where each node in the path has the same value. This path may or may not pass through the root.
递归解决，这篇博客讲得比较清楚：http://www.cnblogs.com/grandyang/p/7636259.html

Implement

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

    int DFS(TreeNode* root, int &res){
        if(!root)
            return 0;
        int l = DFS(root->left, res);
        int r = DFS(root->right, res);
        if(root->left && root->val == root->left->val)
            l = l + 1;
        else 
            l = 0;
        if(root->right && root->val == root->right->val)
            r = r + 1;
        else
            r = 0;
        res = max(res, l + r);
        return max(l, r);
    }
};