LeetCode 337 House Robber III

The thief has found himself a new place for his thievery again. There is only one entrance to this area, called the "root." Besides the root, each house has one and only one parent house. After a tour, the smart thief realized that "all houses in this place forms a binary tree". It will automatically contact the police if two directly-linked houses were broken into on the same night.

Determine the maximum amount of money the thief can rob tonight without alerting the police.

Example 1:

     3    / \   2   3    \   \      3   1

Maximum amount of money the thief can rob = 3 + 3 + 1 = 7.

Example 2:

     3    / \   4   5  / \   \  1   3   1

Maximum amount of money the thief can rob = 4 + 5 = 9.

public int rob(TreeNode root) {         if (root == null) return 0;         if (root.left == null && root.right == null) return root.val;         int left = rob(root.left);         int right = rob(root.right);         int leftSon = 0, rightSon = 0;         if (root.left != null)            leftSon = rob(root.left.left) + rob(root.left.right);         if (root.right != null)            rightSon = rob(root.right.left) + rob(root.right.right);         return Math.max(left + right, root.val + leftSon + rightSon);}