Max Points on a Line

Given n points on a 2D plane, find the maximum number of points that lie on the same straight 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) {
        map<float, int> buf;
        int result = 0;
        for (int i = 0; i < points.size(); i++)
        {
            buf.clear();    
            int duplicate = 1;
            
            for (int j = i+1; j < points.size(); j++)
            {
                if (points[i].x == points[j].x && points[i].y == points[j].y)
                {
                    duplicate++;
                    continue;
                }

                float key = (points[j].x == points[i].x) ? INT_MAX : (float)(points[i].y-points[j].y)/(points[i].x-points[j].x);
                buf[key]++;
            }

            if (buf.size() > 0)
            {
                for (map<float, int>::iterator it = buf.begin(); it != buf.end(); it++)
                {
                    if (it->second + duplicate > result)
                    {
                        result = it->second + duplicate;
                    }
                }
            }
            else
            {
                if (duplicate > result)
                {
                    result = duplicate;
                }
            }
        }

        return result;
    }
};