各种数论模板

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cmath>
 5 using namespace std;
 6 const int MAXN=10001;
 7 int vis[MAXN];
 8 int main()
 9 {
10     int n;
11     scanf("%d",&n);
12     for(int i=2;i<=sqrt(n);i++)
13     {
14         if(vis[i]==0)
15         {
16             for(int j=i*i;j<=n;j=j+i)
17             {
18                 vis[j]=1;
19             }
20         }
21     }
22     for(int i=2;i<=n;i++)
23     {
24         if(vis[i]==0)
25         printf("%d ",i);
26     }
27     return 0;
28 }

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cmath>
 5 using namespace std;
 6 int gcd(int x,int y)
 7 {
 8     if(y==0)
 9     return x;
10     else
11     return gcd(y,x%y);
12 }
13 int main()
14 {
15     int x,y;
16     scanf("%d%d",&x,&y);
17     int gys=gcd(x,y); 
18     printf("%d\n%d",gys,x*y/gys);
19     
20     return 0;
21 }

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cmath>
 4 using namespace std;
 5 int x,y;
 6 int exgcd(int a,int b,int &x,int &y)
 7 {
 8     if(b==0)
 9     {
10         x=1;
11         y=0;
12         return a;
13     }
14     int r=exgcd(b,a%b,x,y);
15     int tmp=x;
16     x=y;
17     y=tmp-(a/b)*y;
18     return r;
19 }
20 int main()
21 {
22     int a,b;
23     scanf("%d%d",&a,&b);
24     exgcd(a,b,x,y);
25     while(x<0)
26     x=x+b;
27     printf("%d",x);
28     return 0;
29 }