Two Pointer Technique on Arrays in DSA Python - Build from Scratch

Two Pointer Technique on Arrays

📖 Scenario: You are working on a simple task to find pairs of numbers in a list that add up to a specific target. This technique is useful in many real-life situations like finding two expenses that sum to a budget limit.

🎯 Goal: Build a program that uses the two pointer technique on a sorted array to find all pairs of numbers that add up to a given target sum.

📋 What You'll Learn

Create a sorted list of integers called numbers with the exact values: [1, 2, 3, 4, 5, 6, 7, 8, 9]

Create a variable called target_sum and set it to 10

Use two pointers named left and right to find pairs in numbers that add up to target_sum

Print each pair found in the format (left_value, right_value)

💡 Why This Matters

🌍 Real World

Finding pairs of expenses that match a budget or pairs of items that fit a weight limit.

💼 Career

Two pointer technique is a common pattern in coding interviews and helps solve problems efficiently without extra space.

1

Create the sorted list of numbers

Create a list called numbers with these exact integers in order: [1, 2, 3, 4, 5, 6, 7, 8, 9]

DSA Python

# Create the list called numbers with the exact values
# Your code here

Hint

Use square brackets to create a list and separate numbers with commas.

2

Set the target sum value

Create a variable called target_sum and set it to the integer 10

DSA Python

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]
# Create the variable target_sum and set it to 10
# Your code here

Hint

Use the assignment operator = to set the value.

3

Use two pointers to find pairs that add to target_sum

Create two variables called left and right. Set left to 0 and right to len(numbers) - 1. Use a while loop with the condition left < right. Inside the loop, calculate the sum of numbers[left] and numbers[right]. If the sum equals target_sum, print the pair as (numbers[left], numbers[right]) and move both pointers inward (left += 1 and right -= 1). If the sum is less than target_sum, move left pointer right (left += 1). If the sum is greater than target_sum, move right pointer left (right -= 1).

DSA Python

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]
target_sum = 10
# Use two pointers left and right to find pairs that add to target_sum
# Your code here

Hint

Remember to move pointers based on comparison of current_sum and target_sum.

4

Print the pairs found

Run the program to print all pairs from numbers that add up to target_sum. The output should show each pair on its own line in the format (left_value, right_value).

DSA Python

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]
target_sum = 10
left = 0
right = len(numbers) - 1
while left < right:
    current_sum = numbers[left] + numbers[right]
    if current_sum == target_sum:
        print((numbers[left], numbers[right]))
        left += 1
        right -= 1
    elif current_sum < target_sum:
        left += 1
    else:
        right -= 1
# Run the program to see the output

Hint

Check the console output for pairs that add to 10.