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Design (LLD)

Compose primitives into a structure that hits required time bounds. The bridge to system design.

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mastery
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Predicted success on the next one
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What you actually need to hold in your head

  • Hash map plus doubly linked list gives O(1) LRU
  • Buckets of equal frequency give LFU
  • Randomised O(1) needs an array and an index map
  • State the invariants before writing methods
Comfortable with these first
Hashing18%Linked List18%Heap / Priority Queue18%
Next in the path
Dynamic Programming

Patterns in this topic

The trigger phrases are what you are training yourself to notice.

Composite Data Structure DesignO(1) amortised for most operations

No single structure hits every bound, so combine them and keep the cross references in sync.

LRU cacheinsert delete getRandom in O(1)

Design (LLD) problems

Ordered by sheet phase, so the early ones are the highest signal.

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Encode and Decode Stringspremium
MDesign (LLD)
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LRU Cache
MDesign (LLD)
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Time Based Key-Value Store
MDesign (LLD)
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Design Twitter
MDesign (LLD)
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Implement Queue using Stacks
EDesign (LLD)
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Insert Delete GetRandom O(1)
MDesign (LLD)
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Random Pick with Weight
MDesign (LLD)
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Design HashMap
EDesign (LLD)
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Design Hit Counterpremium
MDesign (LLD)
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LFU Cache
HDesign (LLD)
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Range Sum Query - Immutable
EDesign (LLD)
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All O(1) Data Structure
HDesign (LLD)
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Design Circular Queue
MDesign (LLD)
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Design In-Memory File Systempremium
HDesign (LLD)
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Design Linked List
MDesign (LLD)
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Design Tic-Tac-Toepremium
MDesign (LLD)
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Design Underground System
MDesign (LLD)
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Implement Stack using Queues
EDesign (LLD)
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Logger Rate Limiterpremium
EDesign (LLD)
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Shuffle an Array
MDesign (LLD)
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Snapshot Array
MDesign (LLD)
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Design a Stack With Increment Operation
MDesign (LLD)