【LeetCode】House Robber III（337）

1. Description

　　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.

2. Answer

/**
 * 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 rob(TreeNode root) {
        if (root == null)
            return 0;
        int first = root.val;
        int second = 0;
        if (root.left != null) {
            first += rob(root.left.left);
            first += rob(root.left.right);
            second += rob(root.left);
        }
        if (root.right != null) {
            first += rob(root.right.left);
            first += rob(root.right.right);
            second += rob(root.right);
        }

        return (first > second) ? first : second;
    }
}