Let’s go deep into Prefix Sum (Pre Sum) from a competitive programming perspective.This is one of the fundamental techniques you’ll repeatedly use in array, string, DP, and number theory problems. What is Prefix Sum? For an array arr[0..n-1], the prefix sum array pre[i] is defined as: That is, the cumulative sum up to index i. … Read more
Greedy algorithms are one of the most elegant problem-solving strategies in computer science. They are fast, intuitive, and often surprisingly effective—but only when applied to the right problems. This guide walks you through the recipe for designing greedy algorithms, the common proof techniques, and the classic patterns you must know. What Is a Greedy Algorithm? … Read more
Check Same binary Tree Leet 100. Same Tree When we first read the “Same Tree” problem, we often think of comparing the traversal results — like inorder, preorder, or postorder — of both trees. That’s a natural and valid idea, but it’s not necessary or ideal in this case. Case 1 : Using one of … Read more
Competitive programming is not just about knowing programming syntax—it’s a blend of logic, speed, and mathematics. Mastering a few essential math tricks can drastically boost your problem-solving skills and efficiency. Let’s explore the most powerful and commonly used math techniques in competitive programming. Prime Numbers A prime number is a number greater than 1 that … Read more
GCD and LCM is a foundational concept in number theory and widely used in areas such as simplifying fractions, cryptography, and solving Diophantine equations. GCD (Greatest Common Divisor) GCD of 12 and 18 So, the GCD is 6 Euclidean Algorithm for GCD This is an efficient method to find GCD: Code Euclidean Algorithm, Why it … Read more
Matrices are fundamental data structures in computer science and mathematics. In competitive programming, matrices are widely used in problems involving 2D grids, dynamic programming, graph algorithms, geometry, and simulations. Basics of Matrices in Python Python doesn’t have a native matrix type. A matrix is typically represented as a list of lists: Concepts Matric Representation Initialisation … Read more
Competitive programming or sport programming is a mind sport involving participants trying to program according to provided specifications. Recursion Recursion is one of the most powerful and elegant tools in programming or even in competitive — but it can seem confusing at first. In this guide, you’ll learn what recursion is, how to identify recursive … Read more
Modulo % Example to show Modulus operator: Refer Extract Last Digit(s) of a Number Digit separation Reverse a number Decimal to binary Using Bitwise Refer Binary to Decimal Using bitwise Array Reverse an Array Array Rotation Method 1 : Using Mod (%) Consider it as circular array and use the property of mod and requires … Read more
Exception Bad Practice Recommended (Good Practice) Way 1 Way 2 Catching a too general Exception is generally considered a bad practice because: Idea Doc String format
Sequential Loops vs Nested Loop Two Sequential Loops (One After Another) Nested Loop Takeway