LeetCode OJ - Max Points on a Line

/**
* Definition for a point.
* struct Point {
*     int x;
*     int y;
*     Point() : x(0), y(0) {}
*     Point(int a, int b) : x(a), y(b) {}
* };
*/
class Solution {
public:
    int maxPoints(vector<Point> &points) {
        int ans = 0;

        vector<Point>::iterator first, second;
        for (first = points.begin(); first != points.end(); first++){
            map<string, int> record_map;
            int same_point = 0, tmp_ans = 0;
            for (second = first + 1; second != points.end(); second++){
                int x = (*second).x - (*first).x, y = (*second).y - (*first).y;
                if (x==0 && y==0){
                    same_point ++;
                    continue;
                }
                /*计算斜率*/
                int g = gcd(x, y);
                if (g){ /*非同一个点*/
                    x = x / g;
                    y = y / g;
                }
                string str_tmp = to_string(x) + " " + to_string(y);
                if (record_map.find(str_tmp) != record_map.end()){
                    record_map[str_tmp] += 1;
                }
                else{
                    record_map[str_tmp] = 1;
                }
                tmp_ans = max(tmp_ans, record_map[str_tmp]);
            }
            ans = max(tmp_ans + 1 + same_point, ans);
        }

        return ans;
    }
private:
    int gcd(int x, int y){
        if (y){
            return gcd(y, x % y);
        }
        else{
            return x;
        }
    }
};