【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 }

 

转载于:https://www.cnblogs.com/Destiny-Gem/p/3983120.html