543.Diameter-of-Binary-Tree

543. Diameter of Binary Tree

题目地址

https://leetcode.com/problems/diameter-of-binary-tree/

题目描述

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.

代码

Approach 1: DFS

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
  int ans = 0;
  public int diameterOfBinaryTree(TreeNode root) {
    dfs(root)
    return ans;
  }

  public int dfs(TreeNode node) {
    if (node == null)    return 0;

    int L = dfs(node.left);
    int R = dfs(node.right);
    ans = Math.max(ans, L + R);

    return Math.max(L, R) + 1;
  }
}