[LeetCode]149 Max Points on a Line

https://oj.leetcode.com/problems/max-points-on-a-line/

http://blog.csdn.net/linhuanmars/article/details/21060933

/**
 * 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) {
    {
        if (points == null || points.length == 0)
            return 0;
        int max = 1;
        for (int i = 0 ; i < points.length - 1 ; i ++)
        {
            // 对于该点，使用一个map保存其余点的斜率
            Map<Double, Integer> map = new HashMap<>();
            
            int samepoints = 0; // Number of same point.
            int x0 = 1; // Number of points with ratio +oo
            
            for (int j = i + 1 ; j < points.length ; j ++)
            {
                if (points[i].x == points[j].x && points[i].y == points[j].y)
                    samepoints ++;
                else if (points[j].x == points[i].x)
                    x0 ++;
                else
                {
                    // 需要特意比对 ratio 为0 的情况是因为double 有 +0.0d 和 -0.0d
                    double ratio = (points[i]. y == points[j].y) ? 
                                   0d :
                                   (double)(points[j].y - points[i].y) / (double)(points[j].x - points[i].x);
                    Integer count = map.get(ratio);
                    if (count == null)  count = 1;
                    count ++;
                    map.put(ratio, count);
                }
            }
            
            max = Math.max(max, x0 + samepoints);
            for (int count : map.values())
                max = Math.max(max, count + samepoints);
        }
        
        return max;
    }
}