# LeetCode-Alg-687-Longest Univalue Path

## LeetCode-Alg-687-Longest Univalue Path

Posted by Jae on May 17, 2019

### 1、题目

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.

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.

### 2、思路

#### 2.2 分析

              4
/ \
4   5
/ \   \
4   4   5


### 3、实现

public class Solution {
private int ans = 0;

public int longestUnivaluePath(TreeNode root) {
univaluePath(root);
return ans;
}

public int univaluePath(TreeNode root){
if (root == null){
return 0;
}

int left = univaluePath(root.left);
int right = univaluePath(root.right);

int leftLen = 0;
int rightLen = 0;
if (root.left != null && root.left.val == root.val){
leftLen += left + 1;
}
if (root.right != null && root.right.val == root.val){
rightLen += right + 1;
}

ans = Math.max(ans, leftLen + rightLen);
return Math.max(leftLen, rightLen);
}
}


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