leetcode 213. 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.

只需要分情况讨论即可， 除去第一家或最后一家，将环断开。
这题又是一个状态的题，抢或不抢两种状态，分别开一个数组存

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

        return Math.max(rob(nums, 0, len-2), rob(nums, 1, len-1));

    }

    public int rob(int[] nums, int start, int end){
        int len = end-start+1;
        int[] r = new int[len];
        int[] s = new int[len];
        int l = start;
        r[0] = nums[l];
        s[0] = 0;
        for(int i =1; i< len; i++){
            r[i] = Math.max(s[i-1]+nums[l+i], r[i-1]);
            s[i] = Math.max(r[i-1], s[i-1]);
        }

        return Math.max(r[len-1], s[len-1]);
    }
}