题解 | #多少个点位于同一直线#

import java.util.*;

/*
 * public class Point {
 *   int x;
 *   int y;
 * }
 */

public class Solution {
    /**
     * 
     * @param points Point类一维数组 
     * @return int整型
     */
    public int maxPoints(Point[] points) {
        int res = 0;
        // write code here
        if (points == null || points.length == 0) {
            return 0;
        }
        if (points.length < 3) {
            return points.length;
        }

        for (int i = 0; i < points.length; i++) {
            int duplicatePoint = 1; //重复的点
            int vartialPoint = 0; //垂直的点，因为垂直的算不出斜率
            Point a = points[i];
            HashMap<Float, Integer> map = new HashMap<Float, Integer>();
            for (int j = 0; j < points.length; j++) {
                if (i == j) {
                    continue;
                }
                Point b = points[j];
                if (b.x == a.x) {  //先算特殊点
                    if (b.y == a.y) {
                        duplicatePoint++;
                    } else {
                        vartialPoint++;
                    }
                } else {  //非特殊点就正常算斜率
                    float k = (float) (a.y - b.y) / (a.x - b.x); //这里一定要强转一下，否则20组样例只能过13组
                    if (map.containsKey(k)) {
                        map.put(k, map.get(k) + 1);
                    } else {
                        map.put(k, 1);
                    }
                }
            }
            int max = vartialPoint;
            //先计算有斜率的和垂直的点 的最大数，不包含初始点
            for (float k : map.keySet()) {
                max = Math.max(map.get(k), max);
            }
            //后将初始点和重复点，一起加上去
            res = Math.max(res, max + duplicatePoint);

        }
        return res;
    }






}