Binary Tree Maximum Path Sum

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.

 

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxPathSum(TreeNode root) {
        int[] max = new int[1];
        max[0] = Integer.MIN_VALUE;
        solve(root, max);
        return max[0];
    }

	private int solve(TreeNode root, int[] max) {
		if (root == null) {
			return 0;
		}
		int left = solve(root.left, max);
		int right = solve(root.right, max);
		int ans = Math.max(root.val, Math.max(root.val+left, root.val+right));
		max[0] = Math.max(max[0], Math.max(ans, root.val+left+right));
		return ans;
	}
}