存储斜率 为了避免精度误差 直接存储分子和分母

        for(int i = 1 ; i <= n ; i ++)
        {
            int xa, ya, xb, yb;
            scanf("%d %d %d %d", &xa, &ya, &xb, &yb);
            int dx = xa - xb;
            int dy = ya - yb;
            if(dx == 0)
            dy = 1;
            else if(dy == 0)
            dx = 1;
            else //第一个放正值 
            {
                if(dx < 0)
                dx = -dx, dy = -dy;
                int t = gcd(abs(dx), abs(dy));
                dx /= t, dy /= t;
            }
            mp[{dx, dy}] ++;
        }