【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 }