#include <stdio.h>
#include <stdlib.h>
char chars[] = {'A','B','C','D'};
void permute(char arr[],int n,int charUsedIndices[],int in );
int main()
{
  int n = 4,array[10]={0,0,0,0,0,0,0,0,0,0};
  char arr[10];
  permute(arr,n,array,0);
  
  return 0;
}
void permute(char arr[],int n,int charUsedIndices[],int in )
{
  
  int i=0;
  if(in == n)
  {
    printf("%s\n",arr);
    return;
  }
  for(i=0;i < n;i++)
  {
    if(charUsedIndices[i] == 1)
      continue;
    
    arr[in] = chars[i];
    charUsedIndices[i] = 1;
    permute(arr,n,charUsedIndices,in+1);
    charUsedIndices[i] = 0;
  }
}