PDSA · Practice

171

Climbing Stairs

PPA · · Python 3

172

House Robber I

PPA · · Python 3

173

House Robber II (circular array)

PPA · · Python 3

174

Maximum subarray sum (Kadane's)

PPA · · Python 3

175

Maximum product subarray

PPA · · Python 3

176

Longest Increasing Subsequence (LIS)

PPA · · Python 3

177

Number of Longest Increasing Subsequences

PPA · · Python 3

178

Russian Doll Envelopes

PPA · · Python 3

179

Coin Change (min coins)

PPA · · Python 3

180

Coin Change II (number of ways)

PPA · · Python 3

181

Word Break I (can string be segmented?)

PPA · · Python 3

182

Word Break II (all segmentations)

PPA · · Python 3

183

Decode Ways (number of ways to decode)

PPA · · Python 3

184

Minimum cost climbing stairs

PPA · · Python 3

185

0/1 Knapsack

PPA · · Python 3

186

Subset sum (can we achieve target?)

PPA · · Python 3

187

Count subsets with given sum

PPA · · Python 3

188

Partition equal subset sum

PPA · · Python 3

189

Minimum subset sum difference

PPA · · Python 3

190

Target sum (assign +/- to elements)

PPA · · Python 3

191

Longest Common Subsequence (LCS)

PPA · · Python 3

192

Longest Common Substring

PPA · · Python 3

193

Edit Distance (Levenshtein)

PPA · · Python 3

194

Shortest Common Supersequence

PPA · · Python 3

195

Distinct subsequences count

PPA · · Python 3

196

Delete operations to make two strings equal

PPA · · Python 3

197

Minimum ASCII delete sum

PPA · · Python 3

198

Wildcard Matching (? and *)

PPA · · Python 3

199

Regular Expression Matching (. and *)

PPA · · Python 3

200

Interleaving String

PPA · · Python 3

121

Shortest path in unweighted graph

PPA · · Python 3

122

Word Ladder (min transformations)

PPA · · Python 3

123

Word Ladder II (all shortest paths)

PPA · · Python 3

124

0-1 BFS (edge weights 0 or 1)

PPA · · Python 3

125

Minimum steps to reach target (Knight moves)

PPA · · Python 3

126

Shortest path in binary matrix

PPA · · Python 3

127

Walls and Gates (fill distances)

PPA · · Python 3

128

Minimum time to infect all nodes

PPA · · Python 3

129

Snakes and Ladders

PPA · · Python 3

130

Jump Game III (can you reach 0?)

PPA · · Python 3

56

Binary search on sorted array

PPA · · Python 3

57

First and last position of element in sorted array

PPA · · Python 3

58

Search in rotated sorted array

PPA · · Python 3

59

Search in rotated sorted array with duplicates

PPA · · Python 3

60

Find the pivot/rotation point

PPA · · Python 3

61

Find minimum in rotated sorted array

PPA · · Python 3

62

Median of two sorted arrays

PPA · · Python 3

63

Kth smallest element in sorted matrix

PPA · · Python 3

64

Capacity to ship packages in D days

PPA · · Python 3

65

Koko Eating Bananas

PPA · · Python 3

66

Aggressive cows (place C cows in N stalls)

PPA · · Python 3

67

Book Allocation Problem

PPA · · Python 3

68

Square root of a number (integer)

PPA · · Python 3

69

Find peak element in array

PPA · · Python 3

70

Search in 2D matrix (row & col sorted)

PPA · · Python 3

71

Find K closest elements to X

PPA · · Python 3

72

Count occurrences of element in sorted array

PPA · · Python 3

73

Find the missing number in sorted array

PPA · · Python 3

74

Allocate minimum number of pages

PPA · · Python 3

75

Nth root of a number

PPA · · Python 3

106

Number of islands

PPA · · Python 3

107

Max area of island

PPA · · Python 3

108

Surrounded regions (flip O's to X's)

PPA · · Python 3

109

Pacific Atlantic Water Flow

PPA · · Python 3

110

Path sum in binary tree (graph view)

PPA · · Python 3

111

All paths from source to target

PPA · · Python 3

112

Word Search in grid

PPA · · Python 3

113

Strongly Connected Components (Kosaraju's)

PPA · · Python 3

114

Strongly Connected Components (Tarjan's)

PPA · · Python 3

115

Articulation points in graph

PPA · · Python 3

116

Bridges in graph

PPA · · Python 3

117

Critical connections in network

PPA · · Python 3

118

Clone a graph

PPA · · Python 3

119

Check if path exists between two nodes

PPA · · Python 3

120

Count paths between source and destination

PPA · · Python 3

131

Single-source shortest path (non-negative weights)

PPA · · Python 3

132

Network delay time

PPA · · Python 3

133

Cheapest flights within K stops

PPA · · Python 3

134

Path with minimum effort

PPA · · Python 3

135

Swim in rising water

PPA · · Python 3

136

Count shortest paths

PPA · · Python 3

137

Minimum cost to connect all points

PPA · · Python 3

138

Shortest path in weighted DAG

PPA · · Python 3

139

Bellman-Ford algorithm (negative weights)

PPA · · Python 3

140

Detect negative weight cycle

PPA · · Python 3

141

Floyd-Warshall (all pairs shortest path)

PPA · · Python 3

142

Reconstruct shortest path (with parent tracking)

PPA · · Python 3

230

Merge Sort

PPA · · Python 3

231

Quick Sort

PPA · · Python 3

232

Binary Search

PPA · · Python 3

233

Count inversions in array

PPA · · Python 3

234

Maximum subarray (D&C approach)

PPA · · Python 3

235

Closest pair of points

PPA · · Python 3

236

Majority element (Boyer-Moore / D&C)

PPA · · Python 3

237

Pow(x, n) — fast exponentiation

PPA · · Python 3

238

Median of medians (deterministic Kth)

PPA · · Python 3

239

Skyline problem

PPA · · Python 3

240

Expression tree evaluation

PPA · · Python 3

201

Unique paths in grid

PPA · · Python 3

202

Unique paths with obstacles

PPA · · Python 3

203

Minimum path sum in grid

PPA · · Python 3

204

Triangle minimum path sum

PPA · · Python 3

205

Maximal square of 1s

PPA · · Python 3

206

Dungeon Game (min health to reach bottom-right)

PPA · · Python 3

207

Cherry Pickup I

PPA · · Python 3

208

Cherry Pickup II (two robots)

PPA · · Python 3

209

Matrix Chain Multiplication

PPA · · Python 3

210

Burst Balloons

PPA · · Python 3

211

Palindrome Partitioning II (min cuts)

PPA · · Python 3

212

Longest Palindromic Subsequence

PPA · · Python 3

213

Longest Palindromic Substring

PPA · · Python 3

214

Strange Printer

PPA · · Python 3

215

Remove boxes

PPA · · Python 3

216

Optimal BST

PPA · · Python 3

217

Stone Merge (minimum cost to merge piles)

PPA · · Python 3

224

Best time to buy & sell stock I (1 transaction)

PPA · · Python 3

225

Best time to buy & sell stock II (unlimited)

PPA · · Python 3

226

Best time to buy & sell stock III (2 transactions)

PPA · · Python 3

227

Best time to buy & sell stock IV (K transactions)

PPA · · Python 3

228

Buy & sell with cooldown

PPA · · Python 3

229

Buy & sell with transaction fee

PPA · · Python 3

218

Diameter of Binary Tree

PPA · · Python 3

219

Binary Tree Maximum Path Sum

PPA · · Python 3

220

House Robber III (on tree nodes)

PPA · · Python 3

221

Unique BSTs (Catalan number via DP)

PPA · · Python 3

222

Unique BSTs II (generate all)

PPA · · Python 3

223

Maximum product of splitted binary tree

PPA · · Python 3

96

Build adjacency list from edge list

PPA · · Python 3

97

DFS traversal (iterative and recursive)

PPA · · Python 3

98

BFS traversal

PPA · · Python 3

99

Detect cycle in undirected graph

PPA · · Python 3

100

Detect cycle in directed graph

PPA · · Python 3

101

Topological Sort (DFS-based)

PPA · · Python 3

102

Topological Sort (BFS / Kahn's Algorithm)

PPA · · Python 3

103

Number of connected components

PPA · · Python 3

104

Bipartite graph check (2-colorable)

PPA · · Python 3

105

Transpose/reverse a directed graph

PPA · · Python 3

155

Activity Selection (max non-overlapping intervals)

PPA · · Python 3

156

Fractional Knapsack

PPA · · Python 3

157

Job Sequencing with deadlines

PPA · · Python 3

158

Minimum platforms needed for trains

PPA · · Python 3

159

Huffman Encoding

PPA · · Python 3

160

Jump Game I (can you reach end?)

PPA · · Python 3

161

Jump Game II (minimum jumps to end)

PPA · · Python 3

162

Gas Station circular tour

PPA · · Python 3

163

Assign cookies to children

PPA · · Python 3

164

Minimum number of arrows to burst balloons

PPA · · Python 3

165

Non-overlapping intervals (remove minimum)

PPA · · Python 3

166

Partition labels

PPA · · Python 3

167

Task Scheduler (CPU with cooldown)

PPA · · Python 3

168

Reorganize string (no adjacent same chars)

PPA · · Python 3

169

Minimum cost to connect ropes

PPA · · Python 3

01

Reverse a Singly Linked List

PPA · · Python 3

02

Reverse a Linked List in K-Groups

PPA · · Python 3

03

Reverse a sublist from position M to N

PPA · · Python 3

04

Detect a cycle in a Linked List

PPA · · Python 3

05

Find the start node of a cycle

PPA · · Python 3

06

Find the middle of a Linked List

PPA · · Python 3

07

Check if Linked List is a palindrome

PPA · · Python 3

08

Merge two sorted Linked Lists

PPA · · Python 3

09

Merge K sorted Linked Lists

PPA · · Python 3

10

Remove Nth node from end of list

PPA · · Python 3

11

Remove duplicates from sorted Linked List

PPA · · Python 3

12

Remove duplicates from unsorted Linked List

PPA · · Python 3

13

Intersection point of two Linked Lists

PPA · · Python 3

14

Add two numbers represented as Linked Lists

PPA · · Python 3

15

Add two numbers represented as Linked Lists (reversed)

PPA · · Python 3

16

Flatten a multilevel Doubly Linked List

PPA · · Python 3

17

Rotate a Linked List by K positions

PPA · · Python 3

18

Sort a Linked List

PPA · · Python 3

19

Clone a Linked List with random pointer

PPA · · Python 3

20

Swap nodes in pairs

PPA · · Python 3

21

Delete a node given only access to that node

PPA · · Python 3

22

Split a Linked List into two halves

PPA · · Python 3

23

Segregate even and odd nodes in Linked List

PPA · · Python 3

24

Check if a linked list is sorted

PPA · · Python 3

25

LRU Cache implementation

PPA · · Python 3

26

LFU Cache implementation

PPA · · Python 3

143

Kruskal's MST

PPA · · Python 3

144

Prim's MST

PPA · · Python 3

145

Minimum cost to connect all cities

PPA · · Python 3

146

Remove max-weight edge keeping graph connected

PPA · · Python 3

147

Number of operations to make network connected

PPA · · Python 3

148

Minimum spanning forest (K components)

PPA · · Python 3

46

Implement Queue using two stacks

PPA · · Python 3

47

Circular Queue implementation

PPA · · Python 3

48

First non-repeating character in a stream

PPA · · Python 3

49

BFS level-order traversal of Binary Tree

PPA · · Python 3

50

Rotten Oranges (multi-source BFS)

PPA · · Python 3

51

01 Matrix (distance to nearest 0)

PPA · · Python 3

52

Sliding Window Maximum (Deque)

PPA · · Python 3

53

Generate Binary Numbers from 1 to N using Queue

PPA · · Python 3

54

Interleave first half and second half of queue

PPA · · Python 3

55

Implement Deque from scratch

PPA · · Python 3

76

Bubble Sort implementation

PPA · · Python 3

77

Selection Sort implementation

PPA · · Python 3

78

Insertion Sort implementation

PPA · · Python 3

79

Merge Sort implementation

PPA · · Python 3

80

Quick Sort implementation

PPA · · Python 3

81

Heap Sort implementation

PPA · · Python 3

82

Counting Sort

PPA · · Python 3

83

Radix Sort

PPA · · Python 3

84

Sort 0s, 1s, 2s (Dutch National Flag)

PPA · · Python 3

85

Sort an array of strings by length

PPA · · Python 3

86

Merge intervals

PPA · · Python 3

87

Meeting rooms II (min rooms needed)

PPA · · Python 3

88

Largest number formed from array

PPA · · Python 3

89

Kth largest element in array

PPA · · Python 3

90

Find K most frequent elements

PPA · · Python 3

91

Sort characters by frequency

PPA · · Python 3

92

Count inversions in array

PPA · · Python 3

93

Nearly sorted array (each element at most K away)

PPA · · Python 3

94

Wiggle sort (a[0] <= a[1] >= a[2]…)

PPA · · Python 3

95

Pancake sorting

PPA · · Python 3

27

Valid Parentheses

PPA · · Python 3

28

Minimum stack (get min in O(1))

PPA · · Python 3

29

Next Greater Element (NGE)

PPA · · Python 3

30

Next Smaller Element

PPA · · Python 3

31

Previous Greater Element

PPA · · Python 3

32

Largest Rectangle in Histogram

PPA · · Python 3

33

Maximal Rectangle in Binary Matrix

PPA · · Python 3

34

Trapping Rain Water

PPA · · Python 3

35

Daily Temperatures

PPA · · Python 3

36

Asteroid Collision

PPA · · Python 3

37

Decode String (e.g. 3[a2[bc]])

PPA · · Python 3

38

Evaluate Reverse Polish Notation

PPA · · Python 3

39

Basic Calculator I (with +, -, parentheses)

PPA · · Python 3

40

Basic Calculator II (with *, /)

PPA · · Python 3

41

Remove K digits to get smallest number

PPA · · Python 3

42

Sliding Window Maximum

PPA · · Python 3

43

Implement stack using two queues

PPA · · Python 3

44

Sort a stack using recursion

PPA · · Python 3

45

Celebrity Problem

PPA · · Python 3

149

Implement DSU with rank & path compression

PPA · · Python 3

150

Redundant connection (find cycle edge)

PPA · · Python 3

151

Accounts merge

PPA · · Python 3

152

Friend circles / provinces

PPA · · Python 3

153

Satisfiability of Equality Equations

PPA · · Python 3

154

Smallest string with swaps

PPA · · Python 3