Coding problems and trade-offs

Solve unfamiliar problems and explain correctness, boundaries, and trade-offs.

Solve a specified problem before changing its requirements

A transaction list, a schedule, or a dependency graph gives you concrete input to work with. Each problem states what to return, how ties and invalid values behave, and which changes would require a different approach.

Keep the reference closed for your first attempt. Produce a solution, walk a small example, explain its cost, then handle the follow-up. The problems reuse the preceding foundations and include separate runnable references for comparison.

CHOOSE YOUR NEXT LESSON

Parts group related chapters. Each lesson has a chapter.lesson address, such as 4.07. Open a title below, or use Next to follow the reading sequence. Within a lesson, On this page lists its sections.

2.01
Choose a coding problem and work through its contract
Scan and remember
2.02
Two sum: remember the useful past
Scan and remember
2.03
Valid anagram: equality of multiplicities
Scan and remember
2.04
Group anagrams: canonical keys
Scan and remember
2.05
Longest unique window: move the boundary forward
Scan and remember
2.06
Minimum covering window: track unmet demand
Scan and remember
2.07
Count target-sum subarrays: differences of prefixes
Scan and remember
2.08
Product except self: combine independent summaries
Scan and remember
2.09
Longest consecutive run: expand only from starts
Scan and remember
2.10
Merge intervals: preserve the covered set
Order and boundaries
2.11
Meeting room capacity: count simultaneous demand
Order and boundaries
2.12
Binary search boundary: find the first true position
Order and boundaries
2.13
Rotated array search: identify the ordered half
Order and boundaries
2.14
Shipping capacity: search a feasible answer
Order and boundaries
2.15
Reverse a linked list: keep the unprocessed suffix reachable
Identity and recursion
2.16
Find where a linked list loops back on itself
Identity and recursion
2.17
Merge sorted lists: splice only a safe frontier
Identity and recursion
2.18
Tree level order: keep the next frontier separate
Identity and recursion
2.19
Validate a BST: carry every ancestor constraint
Identity and recursion
2.20
Lowest common ancestor: return presence as well as a candidate
Identity and recursion
2.21
Tree diameter: return one branch, combine two locally
Identity and recursion
2.22
Dependency order
Graphs and retained state
2.23
Word ladder
Graphs and retained state
2.24
Connectivity under added links
Graphs and retained state
2.25
Shortest path through a grid
Graphs and retained state
2.26
Cheapest route with nonnegative costs
Graphs and retained state
2.27
Top k observations in a stream
Graphs and retained state
2.28
Merge k sorted streams
Graphs and retained state
2.29
Prefix autocomplete
Graphs and retained state
2.30
Search for unique combinations
Search and recurrence
2.31
Find a word without reusing a cell
Search and recurrence
2.32
Minimum coins with a witness
Search and recurrence
2.33
Longest increasing subsequence
Search and recurrence
2.34
Edit distance
Search and recurrence
2.35
Count valid digit decodings
Search and recurrence
2.36
Days until a warmer temperature
Stacks, parsing, and streams
2.37
Largest rectangle in a histogram
Stacks, parsing, and streams
2.38
Parse and evaluate a policy expression
Stacks, parsing, and streams
2.39
Maintain an exact streaming median
Stacks, parsing, and streams
2.40
Explain algorithm invariants and the changes that invalidate them
Consolidate and assess
2.41
Compare coding contracts, return values and complexity
Consolidate and assess
2.42
Run an unfamiliar coding mock
Projects and practical assessment
2.43
Consume inventory events without counting replays twice
Projects and practical assessment