【Leetcode】Binary Tree Maximum Path Sum

最新推荐文章于 2025-12-21 17:04:13 发布

转载最新推荐文章于 2025-12-21 17:04:13 发布 · 174 阅读

文章标签：

#leetcode #Java #ArrayList #TreeNode

本文介绍了一种寻找二叉树中最大路径和的有效算法。通过递归遍历节点并记录最大路径值的方法，实现了从任意节点开始到任意节点结束的最大路径求和。提供了三种不同的Java实现方案。

Given a binary tree, find the maximum path sum.

The path may start and end at any node in the tree.

For example:
Given the below binary tree,

       1
      / \
     2   3

Return 6.

Java：

codeeGanker: http://blog.youkuaiyun.com/linhuanmars/article/details/22969069

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxPathSum(TreeNode root) {
        if(root==null) return 0;
        ArrayList<Integer> res= new ArrayList<Integer>();
        res.add(Integer.MIN_VALUE);
        help(root, res);
        return res.get(0);
    }
    
    private int help(TreeNode root, ArrayList<Integer> res){
        if(root==null) return 0;
        int left=help(root.left, res);
        int right=help(root.right, res);
        int cur=root.val+(left>0?left:0)+(right>0?right:0);
        if(cur>res.get(0)) res.set(0,cur);
        return root.val+Math.max(left,Math.max(right,0));
    }
    
}

另外两种方法：代码略不同
1. http://www.cnblogs.com/lautsie/p/3249723.html

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxPathSum(TreeNode root) {
        if(root==null) return 0;
        int max[] = new int[1];
        max[0] = Integer.MIN_VALUE;
        help(root, max);
        return max[0];
    }
    
    private int help(TreeNode root, int[] max){
        if(root==null) return 0;
        int left=help(root.left, max);
        int right=help(root.right, max);
        int cur=Math.max(root.val,Math.max(left+root.val,right+root.val));
        max[0]=Math.max(max[0],Math.max(cur,left+root.val+right));
        return cur;
    }
    
}

2. http://blog.youkuaiyun.com/fightforyourdream/article/details/16894069