213 House Robber II

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.

思路不是很明白：

用两个范围做，因为是circle，第一种是index from 0 to len - 2

index from 1 to len - 1

find the max

class Solution {
    public int rob(int[] nums) {
        if (nums == null || nums.length == 0 ){ 
            return 0;
        }
        if (nums.length == 1) {
            return nums[0];
        }
        int includeFirst = helper(nums, 0, nums.length - 2);
        int excludeFirst = helper(nums, 1, nums.length - 1);
        return Math.max(includeFirst,excludeFirst);
    }
    public int helper(int[] nums, int start, int end) {
        int prevYes = 0;
        int prevNo = 0;
        for (int i = start; i <= end; i++) {
            int temp = prevNo;
            prevNo = Math.max(prevYes, prevNo);
            prevYes = temp + nums[i];
        }
        return Math.max(prevYes, prevNo);
    }
}