Function that cleans up duplicates in array

Question

I am trying to make a function that cleans out my duplicates of number in my array, but it seems that i cant figure out what i am missing to just remove the duplicate. Just to make it more clear: The function should not become void.

[1,2,3,3,4] -> [1,2,3,4]
[4,2,5,1]->[4,2,5,1]
[32,21,2,5,2,1,21,4]->[32,21,2,5,1,4]

It should not be empty spaces in my array, and the function should return the unique elements in the cleaned array, where cleaned is defined as "non-duplication of integer numbers"

#include <stdio.h>

int generateUniqeList(int *list, int length);

int main()
{
    int list[6] = { 5, 5, 4, 3, 2, 1 };
    int duplicate = generateUniqeList(list, 6);

    for (int i = 0; i < 6; i++)
    {
        printf("%d\n", list[i] - 1); //Here i am able to change the value of the duplicates with the - 1
    }
    getchar();

    return 0;
}


int generateUniqeList(int *list, int length)
{
    int duplicate = 0;

        for (int i = 0; i < length; i++)
        {
            if (list[i] == list[i])
                duplicate = list[i];
        }
    return duplicate;
}

Do you expect this condition `if (list[i] == list[i])` to evaluate to `false` for some values of `i`? — Sergey Kalinichenko, May 05 '17 at 15:22
To remove an int, you will have to shift the whole array an index to the left from the current position that you want to remove. — Module, May 05 '17 at 15:48
@Module assuming you wan't to do it in-place.. I would go with generating a new list. — Eugene Sh., May 05 '17 at 15:50
@EugeneSh that works perfectly fine as well, but won't that require a temporary array to swap all of the elements to the new list array? — Module, May 05 '17 at 15:54
@Module Sure. It will require more memory but the time (and code) complexity can be reduced. — Eugene Sh., May 05 '17 at 16:10

score 1 · Answer 1 · answered May 05 '17 at 16:39

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


void generateUniqeList(int *list, int length);

int main()
{
  int list[6] = { 5, 5, 4, 3, 2, 1 };
  generateUniqeList(list, 6);

  for (int i = 0; i < 6; i++)
  {
    printf("%d", list[i]); 
  //Here i am able to change the value of the duplicates with the - 1
  }
  putchar('\n');

  return 0;
}


void generateUniqeList(int *list, int length){
  int i ,j,k;
  for (i = 0; i < length; i++) {
      for (j = i + 1; j < length;) {
         if (list[j] == list[i]) {
            for (k = j; k < length; k++) {
               list[k] = list[k + 1];
            }
            length--;
         } else
            j++;
      }
   }

}

score 0 · Answer 2 · edited May 23 '17 at 10:31

0

What you are doing is subtracting every int in your list by 1. This will not remove the duplicates. To remove an element from an array, check out: How to remove an element from an array in C?

edited May 23 '17 at 10:31

Community

1
1

answered May 05 '17 at 15:24

score 0 · Answer 3 · answered May 05 '17 at 15:51

The function does not make a sense. For example the condition in this if statement

if (list[i] == list[i])
    duplicate = list[i];

is always true because each object is equal to itself.

And the function does not modify the array.

You can not resize the array but you can gather all unique elements in the beginning of the array and return the number of the unique elements.

Here is a demonstrative program.

#include <stdio.h>

size_t generateUniqeList( int *a, size_t n )
{
    size_t m = 0;

    for ( size_t i = 0; i < n; i++ )
    {
        size_t j = 0;
        while ( j < m && a[j] != a[i] ) j++;

        if ( j == m )
        {
            if ( m != i ) a[m] = a[i];
            ++m;
        }
    }

    return m;
}   

int main(void) 
{
    int list[] = { 5, 5, 4, 3, 2, 1 };
    const size_t N = sizeof( list ) / sizeof( *list );

    for ( size_t i = 0; i < N; i++ ) printf( "%d ", list[i] );
    putchar( '\n' );

    size_t m = generateUniqeList( list, N );

    for ( size_t i = 0; i < m; i++ ) printf( "%d ", list[i] );
    putchar( '\n' );

    return 0;
}

Its output is

5 5 4 3 2 1 
5 4 3 2 1

Function that cleans up duplicates in array

3 Answers3