149. 直线上最多的点数

给定一个二维平面，平面上有 n 个点，求最多有多少个点在同一条直线上。

示例 1:

输入: [[1,1],[2,2],[3,3]]
输出: 3
解释:
^
|
|        o
|     o
|  o  
+------------->
0  1  2  3  4

示例 2:

输入: [[1,1],[3,2],[5,3],[4,1],[2,3],[1,4]]
输出: 4
解释:
^
|
|  o
|     o        o
|        o
|  o        o
+------------------->
0  1  2  3  4  5  6

代码

class Solution {
public:
    int maxPoints(vector& points) {
        int res = 0;
        for (int i = 0; i < points.size(); ++i) {
            map, int> m;
            int duplicate = 1;
            for (int j = i + 1; j < points.size(); ++j) {
                if (points[i].x == points[j].x && points[i].y == points[j].y) {
                    ++duplicate; continue;
                } 
                int dx = points[j].x - points[i].x;
                int dy = points[j].y - points[i].y;
                int d = gcd(dx, dy);
                ++m[{dx / d, dy / d}];
            }
            res = max(res, duplicate);
            for (auto it = m.begin(); it != m.end(); ++it) {
                res = max(res, it->second + duplicate);
            }
        }
        return res;
    }
    int gcd(int a, int b) {
        return (b == 0) ? a : gcd(b, a % b);
    }
};