#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

/*
 Sample midterm question:

 Design an algorithm and write code to remove the duplicate characters
 in a string without using any additional buffer. NOTE: One or two
 additional variables are fine. An extra copy of the array is
 not. FOLLOW UP Write the test cases for this function.

 */


// using NO additional buffer

char* deDup(char str[])
{
    int i = 0,j;
    char ch;
    while((ch = str[i++] )!= '\0')
    {
      j = i;
      while(str[j] != '\0')
        {
	  if(ch == str[j])
            {
	      while(str[j]!='\0') {
                str[j] = str[j+1];
		j++;
	      }
	      i--;
	      break;
            }
	  j++;
        }
    }
    return str;
}


// using additional buffer
// O(n)
char* deDup2(char * str)
{
    int len = strlen(str);
    int ch;
    
    bool hit[256] = { false };
    ch = str[0];
    hit[ch] = true;
    int tail = 1;
    for (int i = 1; i < len; ++i) {
      ch = str[i];
      if (!hit[ch]) {
	str[tail] = ch;
	++tail;
	hit[ch] = true;
      }
    }
    str[tail] = 0;
    return str;
}


int main(int argc, char ** argv) {

  if (argc != 2) {
    fprintf(stderr, "Usage: dedup string\n");
    exit(1);
  }

  char * s1 = argv[1];

  printf("%s:", s1);
  deDup(s1);
  printf("%s\n", s1);

  printf("\nwith boolean array:\n");
  printf("%s:", s1);
  // deDup2(s1);
  printf("%s\n", s1);

  return 0;

}


/*

test cases

1. String does not contain any duplicates, e.g.: abcd
2. String contains all duplicates, e.g.: aaaa
3. Null string / Empty string
4. String with all continuous duplicates, e.g.: aaabbb
5. String with non-contiguous duplicate, e.g.: abababa

*/