DSA topic · Stage 3

Linked Lists interview preparation

Manipulate node relationships without relying on indexed access.

DSA prep Practice 6 questions

Concept

Linked-list tasks test pointer ownership, invariants, and handling of the head and tail.

Complexity lens

Distinguish O(1) rewiring from O(n) traversal and state whether extra nodes are allowed.

Common mistakes

Losing the next pointer
Skipping dummy-node edge cases
Comparing values instead of node identity

Recognition

Decide from constraints, not labels.

These clues narrow the model. They do not replace an invariant or complexity check.

Recognition clues

The task changes links rather than indexed values
Head or tail replacement creates special cases
Cycle, midpoint, or fixed-distance relationships matter

Implementation options

Dummy head for uniform insertion/removal
Previous/current/next rewiring
Fast and slow pointers for relative position or cycle state

Interview behavior

Name pointer ownership before mutation
Save the next edge before rewiring
Draw a two- or three-node example including the head

Patterns that operate on this topic

Two PointersEvery candidate outside the active pointer region has already been resolved or proved unable to improve the answer.Fast & Slow PointersThe pointer separation or relative speed encodes the property; pointer equality means identity, not equal stored values.Heap SelectionFor bounded top-k, the heap contains exactly the best k processed candidates and its root is the weakest retained one.

Representative problems

6 current Linked Lists questions.

Exact active distribution: 4 easy, 1 medium, 1 hard. External records contain metadata and original guidance only.

External catalogUnverified
Reverse Linked List
Protect the next pointer before reversing each edge.
Linked Lists Two Pointers
EasyFree / publicSolve problem
External catalogUnverified
Linked List Cycle
Reason about node identity and relative pointer speed.
Linked Lists Fast & Slow Pointers
EasyFree / publicSolve problem
External catalogUnverified
Merge Two Sorted Lists
Use a sentinel node to keep head handling uniform.
Linked Lists Sorting Two Pointers
EasyFree / publicSolve problem
External catalogUnverified
Merge k Sorted Lists
Keep only the next candidate from each ordered list in the heap.
Linked Lists Heaps Heap Selection
HardFree / publicSolve problem
External catalogUnverified
Middle of the Linked List
Makes relative pointer speed intuitive before harder list problems.
Linked Lists Fast & Slow Pointers
EasyFree / publicSolve problem
External catalogUnverified
Remove Nth Node From End of List
Combines dummy nodes with a fixed pointer distance.
Linked Lists Fast & Slow Pointers
MediumFree / publicSolve problem

Review state

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Review prompts

Which pointer was lost?
Would a dummy node remove a branch?
Did I compare node identity rather than value?

Prerequisites and next step

Graph Thinking

Model relationships explicitly and reason about reachability, order, components, grids, and weighted paths.

Open the roadmap

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