150 problems. 20 patterns. Every interview.
Random grinding builds anxiety. Pattern recognition builds interviews you can walk into calm. This is the deliberate progression — each links straight to LeetCode, in the order we'd solve them.
Connect LeetCode and every one of these you've already solved fills in automatically — then the streak keeps you filling the rest. Start free →
Tier 1 · Foundations
Arrays & Hashing
Trade memory for speed: hash maps turn O(n²) scans into O(n) lookups.
Two Pointers
Walk pointers toward each other to cut a quadratic search down to one pass.
Sliding Window
Grow and shrink a window over the data instead of recomputing every range.
Prefix Sum
Precompute running totals so any range query collapses to one subtraction.
Tier 2 · Core techniques
Binary Search
Halve the search space every step — and learn to spot the hidden monotonic axis.
Stack & Monotonic Stack
Last-in-first-out order solves matching, parsing, and 'next greater' in one sweep.
Linked List
Pointer surgery: reverse, splice, and cycle-detect without losing a node.
Intervals
Sort by start, then sweep: overlap problems become a single ordered pass.
Tier 3 · Structures & strategies
Trees & BST
Recursion's home turf: traverse, rebuild, and validate hierarchical data.
Tries
Prefix trees make 'starts with' queries instant — autocomplete's data structure.
Heaps / Priority Queue
Always know the min or max in O(log n) — the 'top K of anything' workhorse.
Greedy
Prove the locally best choice is globally safe, then never look back.
Tier 4 · Search & state
Backtracking
Explore every branch, undo on failure — controlled brute force with pruning.
Graphs (BFS/DFS)
Grids, networks, dependencies — everything is a graph once you see the edges.
Advanced Graphs
Union-Find, topological order, Dijkstra — the heavy machinery for hard edges.
Bit Manipulation
XOR tricks and bit math: the problems that look like magic until they don't.
Tier 5 · The deep end
1-D Dynamic Programming
Define the subproblem, trust the recurrence — linear DP is a conversation with your past self.
2-D Dynamic Programming
Two moving dimensions, one grid of answers. Where DP earns its reputation.
Math & Geometry
Rotations, spirals, and number theory — careful indexing beats clever formulas.
Design & Simulation
Build the data structure yourself: caches, streams, and systems in miniature.
Watch all 150 fill in as you solve.
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