Binary Tree Maximum Path Sum

题目：

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 4
/
2 3
The highlighted path yields the maximum sum 10

解答：

public class Solution {
    private int maxSum;

    public int getPathSum(TreeNode root) {
        maxSum = Integer.MIN_VALUE;
        findMax(root);
        return maxSum;
    }

    private int findMax(TreeNode p) {
        if(p == null) {
            return 0;
        }

        int left = findMax(p.left);
        int right = findMax(p.right);

        maxSum = Math.max(p.val + left + right, maxSum);
        int ret = p.val + Math.max(left, right);
        return ret > 0? ret:0;
    }


}