Leetcode: House Robber

class Solution {
public:
    int rob(vector<int> &num) {
	if (num.empty())
	{
		return 0;
	}
	if (num.size()==1)
	{
		return num[0];
	}
	int first = num[0];
	int second = num[1];
	int res = max(first, second);
	auto it = num.begin() + 2;
	auto itprev = num.begin() + 1;
	for (; it != num.end();++it,++itprev)
	{
		res = max(max(first + *it, second), second - *itprev + *it);
		first = second;
		second = res;
	}
	return res;
    }
};