543. Diameter of Binary Tree

Given a binary tree, you need to compute the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.

Example:
Given a binary tree 

          1
         / \
        2   3
       / \     
      4   5

 

Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

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

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 class Solution {
11     public int diameterOfBinaryTree(TreeNode root) {
12         int[] globalMax = new int[1];
13         helper(root, globalMax);
14         return globalMax[0] - 1 <= 0 ? 0 : globalMax[0] - 1;
15     }
16     
17     private int helper(TreeNode root, int[] globalMax) {
18         if (root == null) return 0;
19         int leftMaxWithRoot = helper(root.left, globalMax);
20         int leftRightWithRoot = helper(root.right, globalMax);
21         
22         int maxWithRoot = Math.max(leftMaxWithRoot, leftRightWithRoot) + 1;
23         globalMax[0] = Math.max(globalMax[0], leftMaxWithRoot + leftRightWithRoot + 1);
24         return maxWithRoot;
25     }
26 }

 

posted @ 2019-05-20 01:39  北叶青藤  阅读(233)  评论(0)  编辑  收藏  举报