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.

O(n^2)， n次n条直线的便利，每次n条直线遍历都计算当前循环内落点最多的直线是哪条。

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/**
 * Definition for a point.
 * struct Point {
 *     int x;
 *     int y;
 *     Point() : x(0), y(0) {}
 *     Point(int a, int b) : x(a), y(b) {}
 * };
 */
class Solution {
public:
    int maxPoints(vector<Point> &points) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        int cnt = points.size();
        int samePoint = 0;
        int vertical = 0;
        unordered_map<double, int> slopeMap;
        int ret = 0;
        for (int i = 0; i < cnt; i++) {
            samePoint = 1;
            vertical = 0;
            slopeMap.clear();
            
            int x1 = points[i].x, y1 = points[i].y;
            int maxslope = 0;
            for (int j = 0; j < cnt; j++) {
                if (i == j) continue;
                int x2 = points[j].x;
                int y2 = points[j].y;
                
                if (x1 == x2) {
                    if (y1 == y2) {
                        samePoint++;
                    } else {
                        vertical++;
                    }
                }
                
                double slope = (double)(y2 - y1) / (double)(x2 - x1);
                slopeMap[slope] += 1;
                maxslope = max(maxslope, slopeMap[slope]);
            }
            
            ret = max(ret, max(vertical, maxslope) + samePoint);
        }
        
        return ret;

  }

}