124.二叉树中的最大路径和.java

/*
 * @lc app=leetcode.cn id=124 lang=java
 *
 * [124] 二叉树中的最大路径和
 */

// @lc code=start
/**
 * 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) {

        helper(root);
        return max;

    }

    public int helper(TreeNode root){
        if(root==null){
            return 0;
        }

        int left=Math.max(0,helper(root.left));
        int right=Math.max(0,helper(root.right));

        int sum=root.val+left+right;

        max=Math.max(max,sum);
        return root.val+Math.max(left,right);

    }
}
// @lc code=end