lintcode-medium-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.

 

Example

Given 4 points: (1,2), (3,6), (0,0), (1,3).

The maximum number is 3.

 

/**
 * Definition for a point.
 * class Point {
 *     int x;
 *     int y;
 *     Point() { x = 0; y = 0; }
 *     Point(int a, int b) { x = a; y = b; }
 * }
 */
public class Solution {
    /**
     * @param points an array of point
     * @return an integer
     */
    public int maxPoints(Point[] points) {
        // Write your code here
        
        if(points == null || points.length == 0)
            return 0;
        
        int result = 0;
        HashMap<Double, Integer> map = new HashMap<Double, Integer>();
        
        for(int i = 0; i < points.length; i++){
            
            int dup = 1;
            int ver = 0;
            
            for(int j = i + 1; j < points.length; j++){
                if(points[i].x == points[j].x){
                    if(points[i].y == points[j].y)
                        dup++;
                    else
                        ver++;
                }
                else{
                    double slope = (double)(points[j].y - points[i].y) / (double)(points[j].x - points[i].x);
                    
                    if(map.containsKey(slope))
                        map.put(slope, map.get(slope) + 1);
                    else
                        map.put(slope, 1);
                }
            }
            
            int count = 0;
            for(Map.Entry<Double, Integer> entry: map.entrySet()){
                if(entry.getValue() > count)
                    count = entry.getValue();
            }
            
            result = Math.max(result, count + dup);
            result = Math.max(result, ver + dup);
            map.clear();
            
        }
        
        return result;
    }
}