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

Remove Duplicates from Sorted Array Using Two Pointers

📖 Scenario: You have a sorted list of numbers representing daily temperatures recorded over several days. Some temperatures are repeated because the sensor recorded the same temperature multiple times in a row. You want to clean this data by removing duplicate temperatures so that each temperature appears only once, keeping the order intact.

🎯 Goal: Build a program that removes duplicates from a sorted list of numbers using the two-pointer technique. The program should modify the list in place and print the cleaned list without duplicates.

📋 What You'll Learn

Create a list called temperatures with the exact values: [30, 30, 32, 32, 32, 35, 36, 36, 38]

Create a variable called write_index and set it to 1

Use a for loop with variable read_index starting from 1 to iterate over temperatures

Inside the loop, compare temperatures[read_index] with temperatures[write_index - 1]

If they are different, assign temperatures[read_index] to temperatures[write_index] and increment write_index by 1

After the loop, slice temperatures to keep only elements up to write_index

Print the final temperatures list

💡 Why This Matters

🌍 Real World

Cleaning sensor data or logs often requires removing repeated values to simplify analysis.

💼 Career

Understanding two-pointer techniques is useful for optimizing array and list operations in software development.

1

Create the sorted list of temperatures

Create a list called temperatures with these exact values: [30, 30, 32, 32, 32, 35, 36, 36, 38]

DSA Python

# Create the list of temperatures
# Your code here

Hint

Use square brackets to create a list and include the numbers exactly as shown.

2

Set up the write pointer

Create a variable called write_index and set it to 1

DSA Python

temperatures = [30, 30, 32, 32, 32, 35, 36, 36, 38]
# Create the write_index variable
# Your code here

Hint

This variable will track where to write the next unique temperature.

3

Use two pointers to remove duplicates

Use a for loop with variable read_index starting from 1 to iterate over temperatures. Inside the loop, compare temperatures[read_index] with temperatures[write_index - 1]. If they are different, assign temperatures[read_index] to temperatures[write_index] and increment write_index by 1. After the loop, slice temperatures to keep only elements up to write_index.

DSA Python

temperatures = [30, 30, 32, 32, 32, 35, 36, 36, 38]
write_index = 1
# Use a for loop to remove duplicates
# Your code here

Hint

Use the two-pointer technique: one pointer reads through the list, the other writes unique values.

4

Print the cleaned list

Print the temperatures list after removing duplicates using print(temperatures)

DSA Python

temperatures = [30, 30, 32, 32, 32, 35, 36, 36, 38]
write_index = 1
for read_index in range(1, len(temperatures)):
    if temperatures[read_index] != temperatures[write_index - 1]:
        temperatures[write_index] = temperatures[read_index]
        write_index += 1

temperatures = temperatures[:write_index]
# Print the final temperatures list
# Your code here

Hint

Use print(temperatures) to show the cleaned list.