Data Structures & Algorithms Interview Prep
Test & Track Your Readiness

Frequency maps, duplicate detection, anagram grouping — the foundation pattern that unlocks O(n) solutions

Eliminate the inner loop — sort and converge from both ends for O(n) solutions to O(n²) problems

Process subarrays without recomputation — fixed and variable window patterns for subarray problems

When previous elements affect current decisions — brackets, histograms, next greater element

Search space reduction — not just sorted arrays but any problem with a monotonic predicate

Fast/slow pointer tricks — cycle detection, midpoint, k-th from end, reversal in O(1) space

Queue-based level traversal — right-side view, zigzag, shortest path in trees

Recursive tree traversal — path sum, LCA, diameter, max depth, serialize/deserialize

Character-by-character prefix matching — autocomplete, word search, prefix counting

Top-K elements, merge K sorted structures, median of a stream — when you need the max/min fast

Build solutions incrementally, prune when impossible — permutations, subsets, N-queens, Sudoku

DFS/BFS on adjacency structures — islands, connected components, shortest path (unweighted)

Disjoint sets with path compression — group membership, cycle detection, Kruskal's MST

Dependency ordering — course prerequisites, build systems, task scheduling with Kahn's + DFS

Optimal substructure in one dimension — house robber, coin change, climbing stairs, Fibonacci variants

Grid paths, string alignment, subsequences — LCS, edit distance, knapsack, unique paths

Local optimal choices that produce global optimal — intervals, jump game, gas station

XOR tricks, bitmasks, counting bits — power of 2, single number, counting bits