Vijos 1092 全排列

来个水题。。难得的1Y。
 1 #include <cstdio>
 2 #include <cstring>
 3 #include <iostream>
 4 using namespace std;
 5 #define LL __int64
 6 int flag[31],que[31];
 7 LL fact[31];
 8 int n;
 9 LL m;
10 void dfs(LL x,int step)
11 {
12     LL temp = 0;
13     int i;
14     for(i = 1;i <= n;i ++)
15     {
16         if(!flag[i])
17         {
18             if(temp + fact[n-step] >= x)
19             {
20                 flag[i] = 1;
21                 que[step] = i;
22                 dfs(x-temp,step+1);
23                 return ;
24             }
25             temp += fact[n-step];
26         }
27     }
28 }
29 int main()
30 {
31     int i;
32     fact[0] = 1;
33     for(i = 1;i <= 20;i ++)
34     fact[i] = fact[i-1]*i;
35     scanf("%d%I64d",&n,&m);
36     dfs(m,1);
37     for(i = 1;i <= n;i ++)
38     {
39         if(i == 1)
40         printf("%d",que[i]);
41         else
42         printf(" %d",que[i]);
43     }
44     printf("
");
45     return 0;
46 }