尋找平面內共線點數最多的直線和點數

import java.awt.Point;
import java.util.HashSet;
import java.util.Set;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		Point[] points = new Point[5];
		points[0] = new Point(-4, -4);
		points[1] = new Point(-8, -582);
		points[2] = new Point(-3, 3);
		points[3] = new Point(-9, -651);
		points[4] = new Point(9, 591);
		System.out.println(maxPoints(points));
		in.close();
	}

	public static int maxPoints(Point[] points) {
		
		if (points == null)
			return 0;
		if (points.length < 1)
			return 0;
		if (points.length == 1)
			return 1;
		if (points.length == 2)
			return 2;

		//使用hashset 來保存已經處理過的直線的斜率
		Set<Float> set = new HashSet<>();
		Point initPoint;
		int maxCount = 2;
		
		//選取兩個初始點來構建一條直線 用到了兩重循環，循環中 識別已經處理過的直線，避免重複
		for (int i = 0; i < points.length - 1; i++) {
			initPoint = points[i];
			
			for (int j = i + 1; j < points.length; j++) {
				int count = 2;  //計算直線上的點數
				
				//處理重複點情況,如果選擇的兩個初始點重複，則至少有三點共線。
				if (points[j].x == initPoint.x && points[j].y == initPoint.y) {
					if (3 > maxCount)
						maxCount = 3;
					continue;
				}

				//計算斜率 剔除重複 直線 的計算
				float xieLv = countXieLv(initPoint, points[j]);
				if (set.contains(xieLv))
					continue;
				else
					set.add(xieLv);
				
				//查詢其他點 看是否在直線上
				for (int k = 0; k < points.length; k++) {
					if (k == j || k == i)  //跳過初始點
						continue;
					//判斷共線
					if (gongXian(initPoint, points[j], points[k]))
						count++;
				}

				if (count > maxCount)
					maxCount = count;
			}
		}
		return maxCount;
	}

	private static float countXieLv(Point point1, Point point2) {
		float dx = (float) point1.x - point2.x;
		float dy = (float) point1.y - point2.y;
		if (dx == 0)  //斜率無窮大
			return 0.00001f;
		return dy / dx;
	}

	private static boolean gongXian(Point point1, Point point2, Point point3) {  //判斷三點共線
		return (point1.y - point2.y) * (point3.x - point2.x) == (point1.x - point2.x) * (point3.y - point2.y);
	}
}