Two-pointer technique in Data Structures Theory - Mini Project: Build & Apply

Understanding the Two-Pointer Technique

📖 Scenario: Imagine you have a list of numbers representing the ages of people waiting in line. You want to find pairs of people whose ages add up to a specific number, like 50. Using the two-pointer technique helps you do this efficiently.

🎯 Goal: Build a simple example that uses the two-pointer technique to find pairs of numbers in a sorted list that add up to a target sum.

📋 What You'll Learn

Create a sorted list of integers called ages with the values [18, 22, 25, 28, 30, 35, 40]

Create two pointers called left and right to track positions in the list

Use a while loop to move the pointers and find pairs that add up to the target sum

Add a variable called target_sum set to 50

💡 Why This Matters

🌍 Real World

The two-pointer technique is used in real life to quickly find pairs or groups that meet certain conditions, like matching people for activities or balancing budgets.

💼 Career

Understanding this technique is important for software developers and data analysts to write efficient code for searching and matching tasks.

1

Create the sorted list of ages

Create a list called ages with these exact values: [18, 22, 25, 28, 30, 35, 40]

Data Structures Theory

# Create the list of ages
# Your code here

Need a hint?

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

2

Set the target sum and initialize pointers

Create a variable called target_sum and set it to 50. Then create two variables called left and right. Set left to 0 and right to the last index of the ages list.

Data Structures Theory

ages = [18, 22, 25, 28, 30, 35, 40]
# Set target_sum and initialize left and right pointers
# Your code here

Need a hint?

Use len(ages) - 1 to get the last index of the list.

3

Use a while loop to find pairs adding to the target sum

Write a while loop that runs as long as left is less than right. Inside the loop, calculate the sum of ages[left] and ages[right]. If the sum equals target_sum, move both pointers inward by increasing left by 1 and decreasing right by 1. If the sum is less than target_sum, increase left by 1. Otherwise, decrease right by 1.

Data Structures Theory

ages = [18, 22, 25, 28, 30, 35, 40]
target_sum = 50
left = 0
right = len(ages) - 1
# Use a while loop to move pointers and check sums
# Your code here

Need a hint?

Remember to update the pointers based on the comparison of current_sum and target_sum.

4

Complete the logic to record pairs found

Create an empty list called pairs before the loop. Inside the if current_sum == target_sum block, add the tuple (ages[left], ages[right]) to pairs. This will store all pairs that add up to the target sum.

Data Structures Theory

ages = [18, 22, 25, 28, 30, 35, 40]
target_sum = 50
left = 0
right = len(ages) - 1
pairs = []
while left < right:
    current_sum = ages[left] + ages[right]
    if current_sum == target_sum:
        # Add the pair to pairs list
        # Your code here
        left += 1
        right -= 1
    elif current_sum < target_sum:
        left += 1
    else:
        right -= 1

Need a hint?

Use the append() method to add pairs to the list.