leetcode笔记：House Robber II

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