cf B. Permutation

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 using namespace std;
 5
 6 int a[100010];
 7 int main()
 8 {
 9     int n,k;
10     scanf("%d%d",&n,&k);
11     for(int i=1; i<=2*n; i++)
12     {
13         a[i]=i;
14     }
15     for(int i=1; i<=k; i++)
16     {
17         swap(a[2*i-1],a[2*i]);
18     }
19     for(int i=1; i<=2*n; i++)
20     {
21         if(i==1) printf("%d",a[i]);
22         else printf(" %d",a[i]);
23     }
24     printf("\n");
25     return 0;
26 }

http://codeforces.com/contest/359/problem/B

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 using namespace std;
 5
 6 int n,k;
 7
 8 int main()
 9 {
10     while(scanf("%d%d",&n,&k)!=EOF)
11     {
12        printf("%d",k+1);
13        for(int i=1; i<=2*n; i++)
14        {
15            if(i!=k+1) printf(" %d",i);
16        }
17        printf("\n");
18     }
19     return 0;
20 }