Max Points on a Line @LeetCode

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

	package leetcode;
	import java.util.HashMap;
	import java.util.Map;
	/**
	* Solution: get a point, calculate slope with all other points to see the max points on a line for this point.(same slope)
	* After calculate every points, the max value will be answer.
	*
	* map.put((double)Integer.MIN_VALUE, 1); hanlde duplicates like(0,0) (0,0). Actually, MIN_VALUE doesn't matter. just define it.
	*
	* map.put(k, 2); -- there's a new point + points[i] = 2
	* 0.0 + slope --> as (double)0/-1 = -0.0, so here we use 0.0+-0.0 =0.0 to handle this problem, if not, there're 0.0, -0.0 (different).
	*
	* Two important thing in this problem.
	* 1. x == x, slope = Integer.MAX_VALUE
	* 2. duplicate points handling
	*
	* @author jeffwan
	* @date Apr 1, 2014
	*/
	public class MaxPoints {
	public static int maxPoints(Point[] points) {
	if (points == null || points.length == 0) {
	return 0;
	}
	HashMap<Double, Integer> map = new HashMap<Double, Integer>();
	int max = 1; // points[i] itself
	for (int i = 0; i < points.length; i++) {
	map.clear();
	map.put((double)Integer.MIN_VALUE, 1);
	int dup = 0;
	for (int j = i + 1; j < points.length; j++) {
	if (points[j].x == points[i].x && points[j].y == points[i].y) {
	dup++;
	continue;
	}
	double k = points[j].x == points[i].x ? (double) Integer.MAX_VALUE:
	0.0 + (double) (points[j].y - points[i].y) / (double) (points[j].x - points[i].x);
	if (map.containsKey(k)) {
	map.put(k, map.get(k) + 1);
	} else {
	map.put(k, 2);
	}
	}
	// duplicate points should be counted in.
	for (int x : map.values()) {
	if (dup + x > max) {
	max = dup + x;
	}
	}
	}
	return max;
	}
	/*********************************************************************************/
	/*
	* My wrong solution: use slope k as unique identifier. create a HashMap. Calculate all slope between two points.
	* and then find the max value. solve equations n(n-1)/2 = max.
	* But slope can't identify one line! parallel lines also have same slope! I also didn't handle x-x = 0 situation.
	*/
	public int maxPoints2(Point[] points) {
	HashMap<Double, Integer> hashMap = new HashMap<Double, Integer>();
	for (int i = 0; i < points.length; i++) {
	for (int j = i + 1; j < points.length; j++) {
	if (points[j].x - points[i].x == 0) {
	continue;
	}
	double k = (double)(points[j].y - points[i].y) / (double)(points[j].x - points[i].x);
	if (hashMap.containsKey(k)) {
	hashMap.put(k, hashMap.get(k) + 1);
	} else {
	hashMap.put(k, 1);
	}
	}
	}
	int max = Integer.MIN_VALUE;
	for (int x : hashMap.values()) {
	max = Math.max(max, x);
	}
	// solve equations n(n-1)/2 = x
	int i;
	for (i = 0; i < points.length; i++) {
	if (i * (i - 1) / 2 == max) {
	break;
	}
	}
	return i;
	}
	// Point Class
	static class Point {
	int x;
	int y;
	Point() { x = 0; y = 0; }
	Point(int a, int b) { x = a; y = b; }
	}
	}

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