第四题：如果一个字符数组中有重复的字符 如"abbcd" 那么如何编程打印其全排列

  #include <stdio.h>
  
 void permutation(char s[], int b, int e)
 {
     if( (0 <= b) && (b <= e) )
    {
         if( b == e )
         {
             printf("%s\n", s);
         }
         else
         {
             int i = 0;
             
             for(i=b; i<=e; i++)
             {
                 char c = s[b];
                 s[b] = s[i];
                 s[i] = c;
                 
                 permutation(s, b+1, e);
                 
                 c = s[b];
                 s[b] = s[i];
                s[i] = c;
             }
         }
     }
}
 
 int main()
 {
    char s[] = "abcd";
    
     permutation(s, 0, 3);
    
    return 0;
}