Leetcode 124. Binary Tree Maximum Path Sum

Question

Given a binary tree, find the maximum path sum.

For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The path does not need to go through the root.

For example:
Given the below binary tree,

   1
  / \
 2   3

Return 6.

Code

 public int maxPathSum(TreeNode root) {
        return dfs(root).max;
    }

    public TNode dfs(TreeNode root) {
        TNode ret = new TNode(Integer.MIN_VALUE, Integer.MIN_VALUE);
        if (root == null) {
            return ret;
        }
        TNode left = dfs(root.left);
        TNode right = dfs(root.right);

        int cross = Math.max(left.maxS, 0) + Math.max(0, right.maxS) + root.val;

        int maxS = Math.max(Math.max(left.maxS, right.maxS), 0) + root.val;

        int max = Math.max(left.max, right.max);
        ret.maxS = maxS;
        ret.max = Math.max(max, cross);
        return ret;

    }

    class TNode {
        int max;
        int maxS;

        public TNode(int max, int maxS) {
            this.max = max;
            this.maxS = maxS;
        }
    }