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

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;
}
};