/**

* 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 {

// 최대 Path 누적 합

int maxPathSumVal = Integer.MIN_VALUE;

// 시간복잡도: O(n), 공간복잡도: O(h) h as height of tree

public int maxPathSum(TreeNode root) {

maxPathSumChecker(root);

return maxPathSumVal;

}

// 재귀

private int maxPathSumChecker(TreeNode node) {

if (node == null) {

return 0;

}

int leftMax = Math.max(maxPathSumChecker(node.left), 0);

int rightMax = Math.max(maxPathSumChecker(node.right), 0);

maxPathSumVal = Math.max(node.val + leftMax + rightMax, maxPathSumVal);

return node.val + Math.max(leftMax, rightMax);

}

}