1、題目描述

https://leetcode-cn.com/problems/binary-tree-maximum-path-sum/submissions/

2、解題思路：

https://leetcode-cn.com/problems/binary-tree-maximum-path-sum/solution/er-cha-shu-zhong-de-zui-da-lu-jing-he-by-ikaruga/

3、程式碼：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 
 
*/
class Solution {
    int max=Integer.MIN_VALUE;
    public int maxPathSum(TreeNode root) {
        dfs(root);
        return max;
    }

    public int dfs(TreeNode root){
        if(root==null){
            return 0;
        }
        // 左右子樹的最大路徑和是否是正貢獻，非正貢獻就取0
        int leftMax=Math.max(0,dfs(root.left));
        
 
int rightMax=Math.max(0,dfs(root.right));
        // 判斷left->root->right這條路徑是不是和最大的
        max=Math.max(max,root.val+leftMax+rightMax);
        // 選一個單邊最大的
        return root.val+Math.max(leftMax,rightMax);
    }
    
}

。。