【LeetCode】213. House Robber II

题目：
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.
分析：
House Robber的扩展。在一个环形数组（即第一个元素与最后一个原始相邻）中取出不相邻的且和最大的数。
可以分两种情况来考虑：（1）不取第一个元素
                                     （2）不取最后一个元素
最后返回两种情况中的最大值。
代码：

class Solution {public:    int rob(vector<int>& nums) {        int l = nums.size();        if(l == 0)        return 0;        if(l == 1)        return nums[0];        int sum[3];        int max;        for(int i = 0;i<3;i++)        {            sum[i] = 0;        }        for(int i = 0;i<l-1;i++)        {            sum[2] = sum[0]+nums[i];            if(sum[2]<sum[1])            sum[2] = sum[1];            sum[0] = sum[1];            sum[1] = sum[2];        }        max = sum[2];        for(int i = 0;i<3;i++)        {            sum[i] = 0;        }        for(int i = 1;i<l;i++)        {            sum[2] = sum[0]+nums[i];            if(sum[2]<sum[1])            sum[2] = sum[1];            sum[0] = sum[1];            sum[1] =sum[2];        }        if(max<sum[2])        return sum[2];        else return max;    }};