GuideTechnology
18 min read
Fixed-size and variable-size windows over arrays and strings, with running sums, counters and frequency maps. Learn the expand-and-shrink template, why it runs in O(n), and when negative numbers break it.
GuideTechnology
18 min read
Replace nested loops with two indices that move in a controlled way. Learn the opposite-ends and same-direction patterns, why each pointer move is safe, and solve pair sum, container with most water, 3Sum and in-place deduplication.
GuideTechnology
22 min read
Linear and binary search done right (invariants, boundaries and overflow-safe midpoints), lower and upper bound, searching on the answer, the main sorting algorithms and their trade-offs, and how to sort anything in Java with comparators.
GuideTechnology
21 min read
How a heap keeps the smallest or largest item ready in O(1), how insert and remove work in O(log n), how to use Java's PriorityQueue, and how to solve top-K, k-th largest and merge-k-sorted problems. Includes how a heap differs from a BST.
GuideTechnology
22 min read
Tree vocabulary, the four traversals (preorder, inorder, postorder, level-order), recursive and iterative code, and binary search trees: search, insert, and the right way to validate one.
GuideTechnology
24 min read
Learn to think recursively: base cases, the call stack and recursion trees. Then use backtracking (choose, explore, undo) to generate subsets, permutations and combinations, avoid duplicates, prune the search and solve N-Queens.
GuideTechnology
20 min read
How hash tables find things almost instantly, what collisions are, how to use HashMap and HashSet in Java, and the patterns that solve duplicates, two-sum, grouping and counting problems. Includes the equals and hashCode contract.
GuideTechnology
19 min read
Last-in-first-out and first-in-first-out, explained with real examples. Learn the right Java collections (ArrayDeque, not Stack), then solve bracket matching, round-robin scheduling and next-greater-element with a monotonic stack.
GuideTechnology
20 min read
Build singly and doubly linked lists from scratch in Java, learn to reason about pointer changes step by step, and solve reversal, middle-finding, merging and cycle detection with clear diagrams and dry runs.
GuideTechnology
17 min read
How Java strings really work: characters and codes, comparison, immutability and StringBuilder, then the classic problems (palindromes, anagrams, run-length encoding) plus honest notes on Unicode.
GuideTechnology
20 min read
How arrays work in memory, why indexing is instant but inserting is slow, and how to solve the classic array problems: maximum, frequency counting, in-place rotation, moving zeroes and subarray sums.
GuideTechnology
19 min read
Big O explained by counting steps: constant, logarithmic, linear, n log n, quadratic and exponential growth, best, average and worst cases, auxiliary and recursion-stack space, with dry runs you can check yourself.
GuideTechnology
21 min read
Only the Java you need for data structures and algorithms: types and overflow, loops, methods, arrays, strings, a small class, input and output, and the mistakes that trip up almost every beginner.
GuideTechnology
17 min read
How to turn a vague problem statement into a clear plan: pin down inputs, outputs and constraints, list edge cases, write pseudocode, build a brute-force answer first and then improve it.
GuideTechnology
15 min read
What data structures and algorithms are, why employers test them, what you can honestly expect from this free 28-article course, and the repeatable six-step loop you will use on every problem.
CourseTechnology
3 min read
A free, 28-article course that takes you from basic problem solving to independently approaching common interview problems in Java. It explains each idea first, shows it in code you can run, and ends with exercises, solutions, an interview workflow and a study plan.
GuideTechnology
5 min read
DSA is the most feared part of software interviews. The fear mostly comes from learning it badly. Here is a calm, pattern-based way to learn it, with a topic order, daily habits and ways to retain what you solve.
