[LeetCode]Maximum number of points on a straight line in 2d plane

From Here

Solution:

Remember that a line can be represented by y=kx+d, if p1 and p2 are in same line, then y1=x1k+d, y2=kx2+d, so y2-y1=kx2-kx1, so k=(y2-y1)/(x2-x1), then we can apply this formula to check if two points are in same line, however how to handle the duplicate points problem?

So instead to calculate the line with maximum points , we should calculate longest line(maximum ponts) through same point,

public class Solution {

     public  int maxPoints(Point[] points) {

            if (points==null||points.length==0){
                return 0;
            }  

            HashMap<Double, Integer> map=new HashMap<Double, Integer>();;
            int max=1;

            for(int i=0; i<points.length; i++){
                // shared point changed, map should be cleared and server the new point
                map.clear();

                // maybe all points contained in the list are same points,and same points' k is 
                // represented by Integer.MIN_VALUE
                map.put((double)Integer.MIN_VALUE, 1);

                int dup=0;

                for(int j=i+1; j<points.length; j++){
                   if (points[j].x==points[i].x&&points[j].y==points[i].y){
                       dup++;
                       continue;
                   }

                   // look 0.0+(double)(points[j].y-points[i].y)/(double)(points[j].x-points[i].x)
                   // because (double)0/-1 is -0.0, so we should use 0.0+-0.0=0.0 to solve 0.0 !=-0.0
                   // problem

                   // if the line through two points are parallel to y coordinator, then K(slop) is 
                   // Integer.MAX_VALUE
                   double key=points[j].x-points[i].x==0?Integer.MAX_VALUE:0.0+(double)(points[j].y-points[i].y)/(double)(points[j].x-points[i].x);

                   if (map.containsKey(key)){
                       map.put(key, map.get(key)+1);
                   }
                   else{
                      map.put(key, 2);
                   }
               }

              for (int temp: map.values()){
                  // duplicate may exist
                  //all duplicate of the cur point are on the same line
                  if (temp+dup>max){
                      max=temp+dup;
                  }
              }

            }

            return max;
        }
}