687. Longest Univalue Path

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.

Note: The length of path between two nodes is represented by the number of edges between them.

Example 1:

Input:

              5
             / \
            4   5
           / \   \
          1   1   5

 

Output:

2

 

Example 2:

Input:

              1
             / \
            4   5
           / \   \
          4   4   5

 

Output:

2

 

Note: The given binary tree has not more than 10000 nodes. The height of the tree is not more than 1000.

 

找出相同节点相连的路径，求最长的边数和

 

C++（71ms）：

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     int longestUnivaluePath(TreeNode* root) {
13         int res = 0 ;
14         if (root)
15             dfs(root , res) ;
16         return res ;
17         
18     }
19     
20     int dfs(TreeNode* root , int& res){
21         int l = root->left ? dfs(root->left , res) : 0 ;
22         int r = root->right ? dfs(root->right , res) : 0 ;
23         
24         int leftEdge = (root->left && root->left->val == root->val) ? l + 1 : 0 ;
25         int rightEdge = (root->right && root->right->val == root->val) ? r + 1 : 0 ;
26         res = max(res , leftEdge + rightEdge) ;
27         return max(leftEdge , rightEdge) ;
28     }
29 };

 

posted @ 2018-03-16 16:20  __Meng  阅读(118)  评论(0)  编辑  收藏  举报