输出1——n的排列（深度优先搜索）

样例输入：

3

样例输出：

123
132
213
231
312
321

 #include <stdio.h>
 int n;

 void dfs(int step,int* a,int* book)
 {
     int i;
     if(step == n)
     {
         for(i = ;i < n;i++)
         {
             printf("%d",a[i]);
         }
         printf("\n");
         return ;
     }

     for(i = ;i < n;i++)
     {
         if(book[i] == )
         {
             a[step] = i+;
             book[i] = ;
             dfs(step+,a,book);
             book[i] = ;
         }
     }
 }
 int main()
 {
     scanf("%d",&n);
     int a[n+],book[n+],i;
     for(i = ;i < n;i++)
     {
         a[i] = ;
         book[i] = ;
     }
     dfs(,a,book);
     return ;
 }