Free series

DSA for Interviews (Java)

Go in order: each lesson builds on the one before. New lessons every week.

Lesson 1

Count steps, not seconds. The Big-O ladder, space complexity, amortized cost and the constraints trick.

Lesson 2

ArrayList, HashMap, HashSet, ArrayDeque, PriorityQueue and TreeMap: which one to use and when, plus 4 Java traps.

Lesson 3

Base case, call stack, recursion trees and memoization, the foundation for trees, backtracking and DP.

Lesson 4

Digit tricks, GCD, primes, why mod 10⁹+7, fast power, overflow traps and counting tricks, with LeetCode practice.

Bit manipulation · Arrays · Strings · Hashing · Linked lists · Stacks & queues · Two pointers · Sliding window…