[leetcode] House Robber II

和I类似，II变成了环形，即首尾只能取一个。调用两次即可。代码如下：

int rob(vector<int>& nums) {
if(nums.empty())
return 0;
if(nums.size() == 1)
return nums[0];
int val = *prev(nums.end());
nums.pop_back();
int result = robLine(nums);
nums.erase(nums.begin());
nums.push_back(val);
return max(result, robLine(nums));
}
int robLine(vector<int> &num) {
if(num.empty())
return 0;
int pre = 0, cur = num[0];
int result = cur;
for(int i = 1; i < num.size(); ++i){
result = max(result, pre + num[i]);
pre = cur;
cur = result;
}
return result;
}