PYTHON:Pair Sum Problem

Check if there exists a pair of numbers in the list that adds up to a target sum.

IntermediateList Programs
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Python Program Code

This program helps you to learn the fundamental structure and syntax of Python programming.

Try This Code
pair-sum-problem.py
# Program to check if any pair in list sums to target

numbers = list(map(int, input("Enter integers separated by space: ").split()))
target = int(input("Enter target sum: "))

seen = set()
found = False

for x in numbers:
    if target - x in seen:
        found = True
        break
    seen.add(x)

if found:
    print("Found a pair with the given sum.")
else:
    print("No pair with the given sum found.")
Terminal Output
Enter integers separated by space: 1 2 3 4
Enter target sum: 5
Found a pair with the given sum.

Understanding Pair Sum Problem

We use a set to track seen numbers and check for the complement (target - x) in O(1) average time.

Note: To write and run Python programs, you need to set up the local environment on your computer. Refer to the complete article Setting up Python Development Environment. If you do not want to set up the local environment on your computer, you can also use online IDE to write and run your Python programs.

Practical Learning Notes for Pair Sum Problem

This Python program is part of the "List Programs" topic and is designed to help you build real problem-solving confidence, not just memorize syntax. Start by understanding the goal of the program in plain language, then trace the logic line by line with a custom input of your own. Once you can predict the output before running the code, your understanding becomes much stronger.

A reliable practice pattern is to run the original version first, then modify only one condition or variable at a time. Observe how that single change affects control flow and output. This deliberate style helps you understand loops, conditions, and data movement much faster than copying full solutions repeatedly.

For interview preparation, explain this solution in three layers: the high-level approach, the step-by-step execution, and the time-space tradeoff. If you can teach these three layers clearly, you are ready to solve close variations of this problem under time pressure.

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Unique Elements from Both Lists