Max Points on a Line

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

Example 1:

Input: [[1,1],[2,2],[3,3]]
Output: 3
Explanation:
^
|
|        o
|     o
|  o  
+------------->
0  1  2  3  4

Example 2:

Input: [[1,1],[3,2],[5,3],[4,1],[2,3],[1,4]]
Output: 4
Explanation:
^
|
|  o
|     o        o
|        o
|  o        o
+------------------->
0  1  2  3  4  5  6

NOTE: input types have been changed on April 15, 2019. Please reset to default code definition to get new method signature.

class Solution {
    public int maxPoints(int[][] points) {
        if (points == null)
            return 0;

        int solution = 0;
        for (int i = 0; i < points.length; i++) {
            Map<String, Integer> map = new HashMap<>();
            int duplicate = 0;
            int max = 0;
            for (int j = i + 1; j < points.length; j++) {
                int deltaX = points[j][0] - points[i][0];
                int deltaY = points[j][1] - points[i][1];
                if (deltaX == 0 && deltaY == 0) {
                    duplicate++;
                    continue;
                }
                int gcd = gcd(deltaX, deltaY);
                int dX = deltaX / gcd;
                int dY = deltaY / gcd;
                map.put(dX + "," + dY, map.getOrDefault(dX + "," + dY, 0) + 1);
                max = Math.max(max, map.get(dX + "," + dY));
            }
            solution = Math.max(solution, max + duplicate + 1);
        }
        return solution;
    }

    public int gcd(int a, int b) {
        if (b == 0)
            return a;
        return gcd(b, a % b);
    }
}