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.

Ideas:

用一个包含两个数的数组表示结果，第一个数表示包含根节点的值，第二个数表示不包含根节点的值 那么最后比较这两个值，取大的一个

Code:

public int rob(TreeNode root) {
    if (root == null) return 0;

    int[] res = robSub(root);
    return Math.max(res[0], res[1]);
}

private int[] robSub(TreeNode root) {
    if (root == null) {
        return new int[2];
    }

    int[] left = robSub(root.left);
    int[] right = robSub(root.right);

    int[] res = new int[2];
    res[0] = root.val + left[1] + right[1];
    res[1] = Math.max(left[0], left[1]) + Math.max(right[0], right[1]);

    return res;
}