Swap Two Numbers without a Temporary Variable | Explained Step-by-Step | Pen & Paper

Swap Two Numbers without a Temporary Variable | Explained Step-by-Step | Pen & Paper In this video from Pen & Paper, we tackle the classic problem: “Swap Two Numbers” (from GeeksforGeeks). The twist: we do this without using any extra temporary variable. While swapping two variables may seem trivial, doing it without a third variable showcases deeper understanding of arithmetic and bit-wise operations — and is a great talking point in coding interviews. What the problem asks: Given two numbers a and b, swap their values so that a takes b’s value and b takes a’s — but you must not use a third (temporary) variable. Examples: Input: a = 2, b = 3 → After swap: a = 3, b = 2. GeeksforGeeks +1 Input: a = 20, b = 0 → After swap: a = 0, b = 20. GeeksforGeeks In this tutorial we cover: The most common and intuitive approach: using arithmetic operations (a = a + b, b = a – b, a = a – b) — how it works, when it fails (overflow risk), and how to explain it. GeeksforGeeks +1 The bit-wise XOR approach: using a = a ^ b; b = a ^ b; a = a ^ b; — why it works at the binary level, its benefits and pitfalls (readability, CPU cost). GeeksforGeeks +1 A brief mention of the built-in swap functions and why the “no temporary variable” requirement exists mostly for educational/algorithmic insight rather than practical necessity. Stack Overflow Interview-ready explanation: how to present your approach, trade-offs, and when using a temporary variable is actually more readable and safer. Why you should watch this: This problem is often used as a warm-up in interviews or coding corners. Demonstrates your mastery of bit-wise operations and low-level logic, which can differentiate you in tech screens. The video uses a clean “Pen & Paper” style: we’ll visually walk through binary values, draw the transformations step-by-step, and highlight potential pitfalls (e.g., integer overflow, same variable aliasing). Call to action: If you’re preparing for software engineering interviews and want to strengthen your bit-manipulation and algorithmic toolkit — hit Subscribe, visit penpaperpreparation.com for printable notes and more practice problems, and leave a comment with your next topic request!