[leetcode]max-points-on-a-line

题目：Given n points on a 2D plane, find the maximum number of points that lie on the same straight line.

答案：

import java.util.*;

/**
 * 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 length = points.length;
        if(length<3)
            return length;
        int max = 2;
        for(int i=0; i<length; i++) {
            int pointMax = 1;
            int samePoints = 0;
            Point start = points[i];
            HashMap<Double, Integer> map = new HashMap<Double, Integer> ();
            for(int j=i+1; j<length; j++){
                Point end = points[j];
                if(start.x == end.x && start.y == end.y) {
                   samePoints++;
                   continue;
                }
                double k;
                if(start.x == end.x) {
                    k = Float.POSITIVE_INFINITY;
                }else if(start.y == end.y) {
                    k = 0;
                }else{
                    k = (float)(start.y-end.y)/(start.x-end.x);
                }
                 
                if(map.containsKey(k)) {
                    map.put(k, map.get(k)+1);
                }else{
                    map.put(k,2);
                }
                pointMax = Math.max(pointMax, map.get(k));
            }
            pointMax += samePoints;
            max = Math.max(max, pointMax);
        }
        return max;
    }
}