POJ-2689 Prime Distance （两重筛素数，区间平移）

 1 # include<iostream>
 2 # include<cstdio>
 3 # include<cstring>
 4 # include<cstdlib>
 5 # include<algorithm>
 6 using namespace std;
 7 # define ll long long
 8 unsigned mypow(unsigned a,unsigned b,unsigned m)
 9 {
10     if(b==0)
11         return 1;
12     if(b==1)
13         return a%m;
14     ll temp=mypow(a,b/2,m);
15     temp*=temp;
16     temp%=m;
17     if(b&1)
18         temp*=a;
19     temp%=m;
20     return temp;
21 }
22 bool Miller_Rabbin(unsigned x)
23 {
24     if(x==2)
25         return true;
26     for(int i=1;i<=2;++i){
27         unsigned a=rand()%(x-2)+2;
28         if(mypow(a,x-1,x)!=1)
29             return false;
30     }
31     return true;
32 }
33 int main()
34 {
35     unsigned a,b;
36     unsigned l1,l2,r1,r2,t;
37     int minn,maxn;
38     while(scanf("%u%u",&a,&b)!=EOF)
39     {
40         if(a==1)
41             a=2;
42         minn=1000005;
43         maxn=0;
44         l1=l2=r1=r2=a;
45         bool yy=true;
46         for(int i=a;i<=b;++i){
47             if(Miller_Rabbin(i)){
48                 if(yy){
49                     t=l1=r1=a;
50                     yy=false;
51                 }
52                 else{
53                     if(minn>i-t){
54                         minn=i-t;
55                         l1=t;
56                         l2=i;
57                     }
58                     if(maxn<i-t){
59                         maxn=i-t;
60                         r1=t;
61                         r2=i;
62                     }
63                 }
64                 t=i;
65             }
66         }
67         if(maxn==0){
68             printf("There are no adjacent primes.\n");
69         }else
70             printf("%u,%u are closest, %u,%u are most distant.\n",l1,l2,r1,r2);
71     }
72     return 0;
73 }

 1 # include<iostream>
 2 # include<cstdio>
 3 # include<cmath>
 4 # include<map>
 5 # include<vector>
 6 # include<cstring>
 7 # include<algorithm>
 8 using namespace std;
 9 const int N=46340;
10 int pri[N],mark[1000010],cnt;
11 vector<unsigned>v;
12 void init()
13 {
14     cnt=0;
15     fill(mark,mark+N+5,1);
16     for(int i=2;i<=N;++i){
17         if(mark[i])
18             pri[cnt++]=i;
19         for(int j=0;j<cnt&&i*pri[j]<=N;++j){
20             mark[i*pri[j]]=0;
21             if(i%pri[j]==0)
22                 break;
23         }
24     }
25 }
26 void work(unsigned a,unsigned b)
27 {
28     v.clear();
29     if(a==1)
30         ++a;
31     memset(mark,0,sizeof(mark));
32     for(int i=0;i<cnt;++i){
33         if(pri[i]>b)
34             break;
35         for(int c=a/pri[i];c*pri[i]<=b;++c){
36             if(c<=1)
37                 continue;
38             if(c*pri[i]<a)
39                 continue;
40             mark[c*pri[i]-a]=1;
41         }
42     }
43     for(int i=0;i<=b-a;++i){
44         if(mark[i]==0)
45             v.push_back(i+a);
46     }
47 }
48 void solve()
49 {
50     int l=v.size();
51     if(l<2){
52         printf("There are no adjacent primes.\n");
53         return ;
54     }
55     int minn=1<<30,maxn=0;
56     unsigned l1,l2,r1,r2;
57     for(int i=1;i<l;++i){
58         if(minn>v[i]-v[i-1]){
59             minn=v[i]-v[i-1];
60             l1=v[i-1];
61             l2=v[i];
62         }
63         if(maxn<v[i]-v[i-1]){
64             maxn=v[i]-v[i-1];
65             r1=v[i-1];
66             r2=v[i];
67         }
68     }
69     printf("%u,%u are closest, %u,%u are most distant.\n",l1,l2,r1,r2);
70 }
71 int main()
72 {
73     init();
74     unsigned a,b;
75     while(scanf("%u%u",&a,&b)!=EOF)
76     {
77         work(a,b);
78         solve();
79     }
80     return 0;
81 }