Leetcode-543. Diameter of Binary Tree

2024年6月9日 108次阅读

前言：为了后续的实习面试，开始疯狂刷题，非常欢迎志同道合的朋友一起交流。因为时间比较紧张，目前的规划是先过一遍，写出能想到的最优算法，第二遍再考虑最优或者较优的方法。如有错误欢迎指正。博主首发CSDN，mcf171专栏。这次比赛略无语，没想到前3题都可以用暴力解。

博客链接：mcf171的博客

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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.

这个题目采用后序遍历即可。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    int maxLength = 0;
    public int diameterOfBinaryTree(TreeNode root) {
        help(root);
        return maxLength;
    }
    
    public int help(TreeNode root){
        if(root == null) return 0;
        int left = help(root.left);
        int right = help(root.right);
        
        maxLength = Math.max(left + right, maxLength);
        
        return Math.max(left + 1, right + 1);
    }
}

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