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.

O(n) time O(1) space

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public class Solution {
    public int rob(int[] nums) {
        if (nums == null || nums.length == 0) return 0;
        if (nums.length == 1) return nums[0];
        return Math.max(robRange(nums, 0, nums.length - 2), robRange(nums, 1, nums.length - 1));
    }
    
    public int robRange(int[] nums, int low, int high) {
        int prevPrev = 0, prev = 0;
        
        for (int i = low; i <= high; i++) {
            int temp = prev;
            prev = Math.max(prev, prevPrev + nums[i]);
            prevPrev = temp;
        }
        return prev;
    }
}