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.

ret表示垂直x轴线上的点数，dup表示和改点重合的点数。

import java.util.HashMap;
import java.util.Map;
/**
 * 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 {
    public int maxPoints(Point[] points){
        int n = points.length;
        if(n<2)return n;
        
        int ret = 0;
        for(int i = 0; i < n; i++){
            int dup = 1;
            int vtl = 0;
            Map<Float, Integer> map = new HashMap<Float, Integer>();
            Point a = points[i];
            
            for(int j = 0; j < n; j++){
                if(i == j) continue;
                Point b = points[j];
                if(a.x == b.x){
                    if(a.y==b.y)dup++;
                    else vtl++;
                }else{
                    float k = (float)(a.y-b.y)/(a.x-b.x);
                    if(map.get(k)==null)map.put(k,1);
                    else map.put(k,map.get(k)+1);
                }
            }
            
            int max = vtl;
            for(float k:map.keySet()){
                max = Math.max(max, map.get(k));
            }
            ret = Math.max(ret, max+dup);
        }
        return ret;
    }
}