C Exercises: Remove duplicates from an array of integers

Last update on August 09 2025 12:47:03 (UTC/GMT +8 hours)

12. Remove Duplicates from Sorted Array Variants

Write a C program to remove duplicates from a given array of integers.

C Code:

#include <stdio.h>
#include <stdlib.h>
static int remove_duplicates(int* nums, int arr_size)
{
    if (arr_size <= 1) {
        return arr_size;
    }

    int i = 0, j, count = 1;
    while (i < arr_size) {
        for (j = i + 1; j < arr_size && nums[i] == nums[j]; j++) {}
        if (j < arr_size) {
            nums[count++] = nums[j];
        }
        i = j;
    }

    return count;
}

int main(void)
{
    int nums[] = {1,1,2,3,4,4,5,6,6,6};    
    int size = sizeof(nums)/sizeof(nums[0]);
    printf("Original array:\n");
    int i;
    for (i = 0; i < size; i++) {
        printf("%d ", nums[i]);
    }
    int count = remove_duplicates(nums, size);
    printf("\nAfter removing duplicates from the above sorted array:\n");
    for (i = 0; i < count; i++) {
        printf("%d ", nums[i]);
    }
    printf("\n");
    return 0;
}

Sample Output:

Original array:
1 1 2 3 4 4 5 6 6 6 
After removing duplicates from the above sorted array:
1 2 3 4 5 6

Pictorial Presentation:

C Programming: Remove the duplicates from a given array of integers.

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to remove duplicates from a sorted array in-place and return the new length.
Write a C program to remove duplicates from a sorted linked list and display the unique list.
Write a C program to output unique elements from a sorted array after removing duplicates.
Write a C program to implement duplicate removal from a sorted array using a two-pointer approach.

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