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Lucid LeetCode Questions 2026

Browse LeetCode problems frequently asked by Lucid. Filter by difficulty and timeframe to focus your interview prep.

Last updated: 20 Feb 2026

Timeframe

Difficulty

Problem	Difficulty	Frequency	Topics
Valid Parentheses	EASY	75%	StringStack
Collect Coins in a Tree	HARD	100%	ArrayTreeGraph TheoryTopological Sort
Maximum Number of Balls in a Box	EASY	100%	Hash TableMathCounting
Longest Substring Without Repeating Characters	MEDIUM	62.5%	Hash TableStringSliding Window
Min Stack	MEDIUM	62.5%	StackDesign
Lowest Common Ancestor of a Binary Tree	MEDIUM	62.5%	TreeDepth-First SearchBinary Tree
Number of Islands	MEDIUM	75%	ArrayDepth-First SearchBreadth-First SearchUnion-FindMatrix

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