Recursion LeetCode Problems: All 45, With Python Solutions

Every problem in this library that LeetCode tags Recursion — 45 in total, 36 of them with a complete Python solution, a worked example and the time and space complexity of the approach.

45 problems
9 Easy
22 Medium
14 Hard

Recursion problems by difficulty

Problems with a complete Python solution are listed first, then by ascending problem number.

Easy (9)

#	Problem	Difficulty	Topics
21	Merge Two Sorted Lists	Easy	Recursion, Linked List
203	Remove Linked List Elements	Easy	Recursion, Linked List
206	Reverse Linked List	Easy	Recursion, Linked List
231	Power of Two	Easy	Bit Manipulation, Recursion, Math
234	Palindrome Linked List	Easy	Stack, Recursion, Linked List +1
326	Power of Three	Easy	Recursion, Math
342	Power of Four	Easy	Bit Manipulation, Recursion, Math
509	Fibonacci Number	Easy	Recursion, Memoization, Math +1
2094	Finding 3-Digit Even Numbers	Easy	Recursion, Array, Hash Table +2

Medium (22)

#	Problem	Difficulty	Topics
2	Add Two Numbers	Medium	Recursion, Linked List, Math
24	Swap Nodes in Pairs	Medium	Recursion, Linked List
50	Pow(x, n)	Medium	Recursion, Math
143	Reorder List	Medium	Stack, Recursion, Linked List +1
241	Different Ways to Add Parentheses	Medium	Recursion, Memoization, Math +2
390	Elimination Game	Medium	Recursion, Math
394	Decode String	Medium	Stack, Recursion, String
486	Predict the Winner	Medium	Recursion, Array, Math +2
779	K-th Symbol in Grammar	Medium	Bit Manipulation, Recursion, Math
894	All Possible Full Binary Trees	Medium	Tree, Recursion, Memoization +2
1545	Find Kth Bit in Nth Binary String	Medium	Recursion, String, Simulation
1823	Find the Winner of the Circular Game	Medium	Recursion, Queue, Array +2
1922	Count Good Numbers	Medium	Recursion, Math
1969	Minimum Non-Zero Product of the Array Elements	Medium	Greedy, Recursion, Math
2487	Remove Nodes From Linked List	Medium	Stack, Recursion, Linked List +1
2550	Count Collisions of Monkeys on a Polygon	Medium	Recursion, Math
247	Strobogrammatic Number IIPremium	Medium	Recursion, Array, String
255	Verify Preorder Sequence in Binary Search TreePremium	Medium	Stack, Tree, Binary Search Tree +4
439	Ternary Expression ParserPremium	Medium	Stack, Recursion, String
544	Output Contest MatchesPremium	Medium	Recursion, String, Simulation
776	Split BSTPremium	Medium	Tree, Binary Search Tree, Recursion +1
1265	Print Immutable Linked List in ReversePremium	Medium	Stack, Recursion, Linked List +1

Hard (14)

#	Problem	Difficulty	Topics
10	Regular Expression Matching	Hard	Recursion, String, Dynamic Programming
25	Reverse Nodes in k-Group	Hard	Recursion, Linked List
44	Wildcard Matching	Hard	Greedy, Recursion, String +1
60	Permutation Sequence	Hard	Recursion, Math
224	Basic Calculator	Hard	Stack, Recursion, Math +1
233	Number of Digit One	Hard	Recursion, Math, Dynamic Programming
273	Integer to English Words	Hard	Recursion, Math, String
736	Parse Lisp Expression	Hard	Stack, Recursion, Hash Table +1
761	Special Binary String	Hard	Recursion, String
1106	Parsing A Boolean Expression	Hard	Stack, Recursion, String
1808	Maximize Number of Nice Divisors	Hard	Recursion, Math, Number Theory
248	Strobogrammatic Number IIIPremium	Hard	Recursion, Array, String
770	Basic Calculator IV	Hard	Stack, Recursion, Hash Table +2
772	Basic Calculator IIIPremium	Hard	Stack, Recursion, Math +1

Keep exploring

All LeetCode topicsEvery tag with a page of its own, with the number of problems behind each.LeetCode patternsThe techniques themselves, with a Python template and complexity for each.Curated study listsBlind 75, NeetCode 150 and three more, grouped by pattern.Easy problemsStart here when the data structure is new rather than the problem.

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