数学 Codeforces Round #291 (Div. 2) B. Han Solo and Lazer Gun

题目传送门

 /*
     水题，就是用三点共线的式子来判断射击次数
 */
 #include <cstdio>
 #include <cmath>
 #include <string>
 #include <cstring>
 #include <iostream>
 #include <algorithm>
 #include <map>
 #include <set>
 #include <vector>
 using namespace std;
 const int MAXN = 1e3 + ;
 int x[MAXN], y[MAXN];
 bool used[MAXN];
 int main(void)
 {
     //freopen ("B.in", "r", stdin);
     int n, x0, y0;
     while (~scanf ("%d%d%d", &n, &x0, &y0))
     {
         memset (used, , sizeof (used));
         for (int i=; i<=n; ++i)
         {
             scanf ("%d%d", &x[i], &y[i]);
             x[i] -= x0;  y[i] -= y0;
         }
         int cnt = ;
         for (int i=; i<=n; ++i)
         {
             if (!used[i])
             {
                 cnt++;
                 for (int j=i; j<=n; ++j)
                 {
                     if (!used[j] && (x[i] * y[j] == x[j] * y[i]))
                         used[j] = ;
                 }
             }
         }
         printf ("%d\n", cnt);
     }
     return ;
 }