LeetCode OJ-- Max Points on a Line **@

https://oj.leetcode.com/problems/max-points-on-a-line/

给n多个二维平面上的点，求其中在同一条直线上点的最大数

细节题，也挺考脑力的

class Solution {
public:
    int maxPoints(vector<Point> &points) {
        if(points.size() == 0 || points.size() == 1 || points.size() == 2)
            return points.size();
        
        map<double,int> lines; 
        int ans = 0;
        
        for(int i = 0; i< points.size(); i++)
        {
            lines.clear();//only use 斜率 represent a line, because from point i, they have a same point, so they are the same
            lines.insert(make_pair(INT_MIN,1)); //如果只有相同的点的时候，应该把点 i 算在内
            int dup = 0;
            
            for(int j = i + 1; j< points.size(); j++)
            {
                if((points[i].x == points[j].x) && (points[i].y == points[j].y))
                {
                    dup++; //record the same point with points[i], then every line + 1
                    continue;
                }
                //calc lines
                double _k = ((points[i].x == points[j].x) ? INT_MAX : (points[i].y - points[j].y)*1.0/(points[i].x - points[j].x));
                if(lines.count(_k)!=0)
                    lines[_k]++;
                else
                    lines.insert(make_pair(_k,2));
            }
            for(map<double,int>::iterator itr = lines.begin(); itr != lines.end(); itr++)
            {
                if(ans < dup + itr->second)
                    ans = dup + itr->second;
            }
        }
        return ans;
    }
};