Remove Duplicates from Sorted Array Two Pointer in DSA C - Build from Scratch

Remove Duplicates from Sorted Array Two Pointer

📖 Scenario: You have a sorted list of numbers that may contain duplicates. You want to clean it up so that each number appears only once, keeping the order intact.

🎯 Goal: Build a program that removes duplicates from a sorted array using the two-pointer technique and prints the cleaned array.

📋 What You'll Learn

Create an integer array called nums with the exact values: 1, 1, 2, 2, 3, 4, 4, 5

Create an integer variable called length and set it to the size of nums

Use two integer pointers i and j to remove duplicates in-place

Print the array after removing duplicates, showing only unique elements separated by spaces

💡 Why This Matters

🌍 Real World

Removing duplicates from sorted data is common in cleaning up lists like contact numbers, product IDs, or timestamps.

💼 Career

Understanding two-pointer techniques and in-place array modification is useful for coding interviews and efficient data processing.

1

Create the sorted array

Create an integer array called nums with these exact values: 1, 1, 2, 2, 3, 4, 4, 5.

DSA C

# Create the array nums with the given values
// Your code here

Hint

Use int nums[] = { ... }; to create the array with the exact numbers.

2

Set the length of the array

Create an integer variable called length and set it to the number of elements in nums using sizeof(nums) / sizeof(nums[0]).

DSA C

int nums[] = {1, 1, 2, 2, 3, 4, 4, 5};
// Create length variable to hold the size of nums
// Your code here

Hint

Use sizeof(nums) / sizeof(nums[0]) to get the number of elements.

3

Remove duplicates using two pointers

Use two integer variables i and j. Initialize i to 0. Use a for loop with j from 1 to length - 1. Inside the loop, if nums[j] is not equal to nums[i], increment i and set nums[i] = nums[j]. After the loop, update length to i + 1.

DSA C

int nums[] = {1, 1, 2, 2, 3, 4, 4, 5};
int length = sizeof(nums) / sizeof(nums[0]);
// Remove duplicates using two pointers i and j
// Your code here

Hint

Use i to track the position of unique elements and j to scan through the array.

4

Print the array after removing duplicates

Use a for loop with variable k from 0 to length - 1. Inside the loop, print nums[k] followed by a space. After the loop, print a newline.

DSA C

int nums[] = {1, 1, 2, 2, 3, 4, 4, 5};
int length = sizeof(nums) / sizeof(nums[0]);
int i = 0;
for (int j = 1; j < length; j++) {
    if (nums[j] != nums[i]) {
        i++;
        nums[i] = nums[j];
    }
}
length = i + 1;
// Print the unique elements in nums
// Your code here

Hint

Use printf("%d ", nums[k]); inside the loop and printf("\n"); after the loop.