House Robber II

Note: This is an extension of House Robber.

After robbing those houses on that street, the thief has found himself a new place for his thievery so that he will not get too much attention. This time, all houses at this place are arranged in a circle. That means the first house is the neighbor of the last one. Meanwhile, the security system for these houses remain the same as for those in the previous street.

Given a list of non-negative integers representing the amount of money of each house, determine the maximum amount of money you can rob tonight without alerting the police.

Credits:Special thanks to @Freezen for adding this problem and creating all test cases.

Solution

public class Solution {
     public int rob(int[] nums) {
        if (nums == null || nums.length == 0) return 0;
        if (nums.length == 1) return nums[0];

        int one = rob(nums, 0, nums.length - 2);
        int two = rob(nums, 1, nums.length - 1);
        return Math.max(one, two);
    }

    private int rob(int[] nums, int i, int j) {
        if (i == j) return nums[i];
        int[] dp = new int[j - i + 1];
        dp[0] = nums[i];
        dp[1] = nums[i] > nums[i + 1] ? nums[i] : nums[i + 1];

        for (int runner = i+2; runner <= j; runner++) {
            dp[runner - i] = Math.max(dp[runner - i - 1], dp[runner - i - 2] + nums[runner]);
        }

        return dp[j - i];
    }
}