**一. 题目描述** 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. **二. 题目分析** 该House Robber的升级版，只是增加了一点条件，即第一个element 和最后一个element不能同时出现，则需分为两种情况：  第一种情况: 不包括最后一个element；  第二种情况: 不包括第一个element；  两者的最大值即为全局最大值。 **三. 示例代码** ~~~ class Solution { public: int rob(vector<int>& nums) { if (nums.size() == 0) return 0; if (nums.size() == 1) return nums[0]; return max(rob(nums, 0, nums.size()-1), rob(nums, 1, nums.size())); } int rob(vector<int> &nums, int start, int end) { int a = 0, b = 0; for (int i = start; i < end; i++) { int m = max(b, a+nums[i]); a = b; b = m; } return b; } }; ~~~ **四. 小结** 无