dfs——n的全排列（回溯）

 #include <iostream>
 #include <cstring>
 #include <string>
 #include <map>
 #include <set>
 #include <algorithm>
 #include <fstream>
 #include <cstdio>
 #include <cmath>
 #include <stack>
 #include <queue>
 #define lson l,m,rt<<1
 #define rson m+1,r,rt<<1|1
 using namespace std;
 const double Pi=3.14159265358979323846;
 typedef long long ll;
 const int MAXN=+;
 const int dx[]={,,,,-};
 const int dy[]={,-,,,};
 const int INF = 0x3f3f3f3f;
 const int NINF = 0xc0c0c0c0;
 const ll mod=1e9+;
 int n;
 int flag[MAXN],a[MAXN];
 int cnt=;
 int t;

 void dfs(int t)
 {
     if(t==)
     {
         for(int i=;i<=n;i++)
         {
             cout << a[i]<<" ";
         }
         cout <<endl;
         return;
     }
     for(int i=;i<=n;i++)
     {
         if(flag[i]==)
         {
             flag[i]=;
             a[cnt++]=i;
             //cout <<a[cnt-1]<<" ";
             dfs(t-);
             cnt--;flag[i]=;
         }

     }
 }
 int main()
 {
     while(scanf("%d",&n)&&n)
     {
         t=n;
         dfs(t);
     }
     return ;
 }