【POJ3006】Dirichlet's Theorem on Arithmetic Progressions（素数筛法）

简单的暴力筛法就可。

 #include <iostream>
 #include <cstring>
 #include <cmath>
 #include <cctype>
 #include <cstdio>
 #include <cmath>
 #include <algorithm>
 #include <numeric>
 using namespace std;

 const int N = , M = ;
 bool is[N]; int prm[M];
 int getprm (int n) {
     int i, j, k = ;
     int s, e = (int)(sqrt (0.0 + n) + );
     memset (is, , sizeof(is));
     prm[k ++] = ; is[] = is[] = ;
     for (i = ; i < n; i += ) is[i] = ;
     for (i = ; i < e; i += ) {
         if (is[i]) {
             prm[k ++] = i;
             for (s = i * , j = i * i; j < n; j += s) {
                 is[j] = ;
             }
         }
     }
     for (; i < n; i += ) {
         if (is[i]) prm[k ++] = i;
     }
     return k;
 }

 int main () {
     ios :: sync_with_stdio(false);
     //freopen("out.txt", "w", stdout);
     getprm();
     /*for (int i = 0 ; i < 78499; ++ i) {
         cout << i  << " : " << prm[i] << endl;
     }*/
     long long a, d, n;
     long long cnt = , cur = ;
     while (cin >> a >> d >> n) {
         if (a ==  && d ==  && n == ) break;
         cnt =  ;
         while () {
             if (binary_search(prm, prm + , a)) {
                 cnt ++;
                 if (cnt == n) break;
             }
             a += d;
             //cout << "step: " << cnt << " " << a << endl;
         }
         cout << a << endl;
     }
     return ;
 }