【POJ3006】Dirichlet's Theorem on Arithmetic Progressions（素数筛法）
简单的暴力筛法就可。
1 #include <iostream> 2 #include <cstring> 3 #include <cmath> 4 #include <cctype> 5 #include <cstdio> 6 #include <cmath> 7 #include <algorithm> 8 #include <numeric> 9 using namespace std; 10 11 const int N = 1000005, M = 500005; 12 bool is[N]; int prm[M]; 13 int getprm (int n) { 14 int i, j, k = 0; 15 int s, e = (int)(sqrt (0.0 + n) + 1); 16 memset (is, 1, sizeof(is)); 17 prm[k ++] = 2; is[0] = is[1] = 0; 18 for (i = 4; i < n; i += 2) is[i] = 0; 19 for (i = 3; i < e; i += 2) { 20 if (is[i]) { 21 prm[k ++] = i; 22 for (s = i * 2, j = i * i; j < n; j += s) { 23 is[j] = 0; 24 } 25 } 26 } 27 for (; i < n; i += 2) { 28 if (is[i]) prm[k ++] = i; 29 } 30 return k; 31 } 32 33 int main () { 34 ios :: sync_with_stdio(false); 35 //freopen("out.txt", "w", stdout); 36 getprm(1000000); 37 /*for (int i = 0 ; i < 78499; ++ i) { 38 cout << i << " : " << prm[i] << endl; 39 }*/ 40 long long a, d, n; 41 long long cnt = 0, cur = 0; 42 while (cin >> a >> d >> n) { 43 if (a == 0 && d == 0 && n == 0) break; 44 cnt = 0 ; 45 while (1) { 46 if (binary_search(prm, prm + 78499, a)) { 47 cnt ++; 48 if (cnt == n) break; 49 } 50 a += d; 51 //cout << "step: " << cnt << " " << a << endl; 52 } 53 cout << a << endl; 54 } 55 return 0; 56 }
