编程题：二叉树的最大距离

import java.util.*;

public class Main{
    
    public static class TreeNode{
        TreeNode left;
        TreeNode right;
        int      val;
        
        public TreeNode(int val){
            this.val = val;
        }
    }
    public static class ReturnType{
        int maxLength;
        int height;
        
        public ReturnType(int maxLength,int height ){
            this.maxLength = maxLength;
            this.height    = height;
        }
       
    }
    
    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        String line = scanner.nextLine();
        String[] arrLine =  line.split(" ");
        int n    = Integer.valueOf(arrLine[0]);
        int root = Integer.valueOf(arrLine[1]);
        TreeNode[] arrNode = new TreeNode[n];
        for(int i=0;i<n;i++){
            arrNode[i] = new TreeNode(i+1);
        }
        for(int i=0;i<n;i++){
            String newline = scanner.nextLine();
            arrLine =  newline.split(" ");
            int head  = Integer.valueOf(arrLine[0]);
            int left  = Integer.valueOf(arrLine[1]);
            int right = Integer.valueOf(arrLine[2]);
            if(left!=0){
                arrNode[head-1].left = arrNode[left-1];
            }
            if(right!=0){
                arrNode[head-1].right = arrNode[right-1];
            }
        }
        int res = getMaxLength(arrNode[root-1]).maxLength;
        System.out.println(res);
        
    }
    
    public static ReturnType getMaxLength(TreeNode root){
        if(root == null){
            return new ReturnType(0,0);
        }
        
        ReturnType leftData = getMaxLength(root.left);
        ReturnType rightData = getMaxLength(root.right);
        int height = Math.max(leftData.height,rightData.height)+1;
        int MaxChildLength = Math.max(leftData.maxLength,rightData.maxLength);
        int TwoChildLength = leftData.height+rightData.height+1;
        return new ReturnType(Math.max(MaxChildLength,TwoChildLength),height);
    }
    
    
}

首先分析当前头结点，最大距离可能的情况

• 右子树的最大距离
• 左子树的最大距离
• 右子树深度+左子树深度+1

因此需要返回的信息是：
以该点为头结点时：

• 当前最大距离
• 深度

每次判断出最大距离的三个情况中最大的
还要计算当前深度，为左子树右子树偏大的深度+1