150 Curated DSA Problems — ML Engineer Interview Prep

Ordered by priority (top patterns = most frequently tested for ML/data roles). All problem IDs are LeetCode numbers. Do in Python.

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1. Arrays & Hashing (Highest priority — ~20 problems)

1. LC 1 — Two Sum
2. LC 217 — Contains Duplicate
3. LC 242 — Valid Anagram
4. LC 49 — Group Anagrams
5. LC 347 — Top K Frequent Elements
6. LC 238 — Product of Array Except Self
7. LC 128 — Longest Consecutive Sequence
8. LC 271 — Encode and Decode Strings
9. LC 36 — Valid Sudoku
10. LC 454 — 4Sum II
11. LC 383 — Ransom Note
12. LC 1512 — Number of Good Pairs
13. LC 692 — Top K Frequent Words
14. LC 895 — Maximum Frequency Stack
15. LC 41 — First Missing Positive
16. LC 560 — Subarray Sum Equals K
17. LC 953 — Verifying an Alien Dictionary
18. LC 496 — Next Greater Element I
19. LC 1502 — Can Make Arithmetic Progression
20. LC 1010 — Pairs of Songs With Total Durations Divisible by 60

2. Two Pointers (~10 problems)

21. LC 125 — Valid Palindrome
22. LC 167 — Two Sum II (sorted array)
23. LC 15 — 3Sum
24. LC 11 — Container With Most Water
25. LC 42 — Trapping Rain Water
26. LC 283 — Move Zeroes
27. LC 26 — Remove Duplicates from Sorted Array
28. LC 344 — Reverse String
29. LC 977 — Squares of a Sorted Array
30. LC 88 — Merge Sorted Array

3. Sliding Window (~12 problems)

31. LC 121 — Best Time to Buy and Sell Stock
32. LC 3 — Longest Substring Without Repeating Characters
33. LC 424 — Longest Repeating Character Replacement
34. LC 567 — Permutation in String
35. LC 76 — Minimum Window Substring
36. LC 239 — Sliding Window Maximum
37. LC 209 — Minimum Size Subarray Sum
38. LC 643 — Maximum Average Subarray I
39. LC 1004 — Max Consecutive Ones III
40. LC 1493 — Longest Subarray of 1's After Deleting One Element
41. LC 30 — Substring with Concatenation of All Words
42. LC 992 — Subarrays with K Different Integers

4. Stack (~8 problems)

43. LC 20 — Valid Parentheses
44. LC 155 — Min Stack
45. LC 150 — Evaluate Reverse Polish Notation
46. LC 22 — Generate Parentheses
47. LC 739 — Daily Temperatures
48. LC 853 — Car Fleet
49. LC 84 — Largest Rectangle in Histogram
50. LC 71 — Simplify Path

5. Binary Search (~8 problems)

51. LC 704 — Binary Search
52. LC 74 — Search a 2D Matrix
53. LC 875 — Koko Eating Bananas
54. LC 153 — Find Minimum in Rotated Sorted Array
55. LC 33 — Search in Rotated Sorted Array
56. LC 981 — Time Based Key-Value Store
57. LC 4 — Median of Two Sorted Arrays
58. LC 162 — Find Peak Element

6. Linked List (~10 problems)

59. LC 206 — Reverse Linked List
60. LC 21 — Merge Two Sorted Lists
61. LC 143 — Reorder List
62. LC 19 — Remove Nth Node From End of List
63. LC 138 — Copy List with Random Pointer
64. LC 2 — Add Two Numbers
65. LC 141 — Linked List Cycle
66. LC 287 — Find the Duplicate Number
67. LC 146 — LRU Cache
68. LC 23 — Merge k Sorted Lists

7. Trees (High priority for interviews — ~18 problems)

69. LC 104 — Maximum Depth of Binary Tree
70. LC 226 — Invert Binary Tree
71. LC 100 — Same Tree
72. LC 572 — Subtree of Another Tree
73. LC 235 — Lowest Common Ancestor of a BST
74. LC 102 — Binary Tree Level Order Traversal
75. LC 199 — Binary Tree Right Side View
76. LC 1448 — Count Good Nodes in Binary Tree
77. LC 98 — Validate Binary Search Tree
78. LC 230 — Kth Smallest Element in a BST
79. LC 105 — Construct Binary Tree from Preorder and Inorder
80. LC 124 — Binary Tree Maximum Path Sum
81. LC 297 — Serialize and Deserialize Binary Tree
82. LC 543 — Diameter of Binary Tree
83. LC 110 — Balanced Binary Tree
84. LC 108 — Convert Sorted Array to BST
85. LC 617 — Merge Two Binary Trees
86. LC 112 — Path Sum

8. Heap / Priority Queue (Very relevant — ~10 problems)

87. LC 703 — Kth Largest Element in a Stream
88. LC 1046 — Last Stone Weight
89. LC 973 — K Closest Points to Origin
90. LC 215 — Kth Largest Element in an Array
91. LC 621 — Task Scheduler
92. LC 355 — Design Twitter
93. LC 295 — Find Median from Data Stream
94. LC 767 — Reorganize String
95. LC 1642 — Furthest Building You Can Reach
96. LC 23 — Merge k Sorted Lists (revisit via heap)

9. Backtracking (~8 — light coverage, still asked occasionally)

97. LC 78 — Subsets
98. LC 39 — Combination Sum
99. LC 46 — Permutations
100. LC 90 — Subsets II
101. LC 40 — Combination Sum II
102. LC 79 — Word Search
103. LC 131 — Palindrome Partitioning
104. LC 17 — Letter Combinations of a Phone Number

10. Graphs — BFS/DFS only (Enough for ML roles — ~14 problems)

105. LC 200 — Number of Islands
106. LC 133 — Clone Graph
107. LC 695 — Max Area of Island
108. LC 417 — Pacific Atlantic Water Flow
109. LC 130 — Surrounded Regions
110. LC 994 — Rotting Oranges
111. LC 286 — Walls and Gates
112. LC 207 — Course Schedule
113. LC 210 — Course Schedule II
114. LC 684 — Redundant Connection
115. LC 323 — Number of Connected Components
116. LC 261 — Graph Valid Tree
117. LC 127 — Word Ladder
118. LC 743 — Network Delay Time

11. 1-D Dynamic Programming (High priority — ~15 problems)

119. LC 70 — Climbing Stairs
120. LC 746 — Min Cost Climbing Stairs
121. LC 198 — House Robber
122. LC 213 — House Robber II
123. LC 5 — Longest Palindromic Substring
124. LC 647 — Palindromic Substrings
125. LC 91 — Decode Ways
126. LC 322 — Coin Change
127. LC 152 — Maximum Product Subarray
128. LC 139 — Word Break
129. LC 300 — Longest Increasing Subsequence
130. LC 416 — Partition Equal Subset Sum
131. LC 62 — Unique Paths
132. LC 55 — Jump Game
133. LC 1143 — Longest Common Subsequence

12. 2-D DP (~8 — moderate priority)

134. LC 1143 — Longest Common Subsequence (already above; alt: 72 Edit Distance)
135. LC 72 — Edit Distance
136. LC 97 — Interleaving String
137. LC 329 — Longest Increasing Path in a Matrix
138. LC 115 — Distinct Subsequences
139. LC 174 — Dungeon Game
140. LC 64 — Minimum Path Sum
141. LC 63 — Unique Paths II

13. Greedy (~6)

142. LC 53 — Maximum Subarray
143. LC 55 — Jump Game (revisit)
144. LC 45 — Jump Game II
145. LC 134 — Gas Station
146. LC 763 — Partition Labels
147. LC 435 — Non-overlapping Intervals

14. Intervals (Your known gap — cover fully, ~6)

148. LC 57 — Insert Interval
149. LC 56 — Merge Intervals
150. LC 435 — Non-overlapping Intervals (revisit)
151. LC 252 — Meeting Rooms
152. LC 253 — Meeting Rooms II
153. LC 1851 — Minimum Interval to Include Each Query

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Deliberately excluded (CP-territory, low ROI for ML interviews)

• Segment trees, Fenwick trees, tries (except if asked for autocomplete-style system design)
• Heavy number theory (modular exponentiation, sieve variants, combinatorics beyond basics)
• Advanced string algorithms (KMP, Z-function, suffix arrays)
• Game theory / Nim-style problems
• Bitmask DP, digit DP

Suggested pace

• 5–6 problems/week alongside your ML/HOML work → ~150 problems in ~26–28 weeks
• If compressing for October: 8–10/week → done in ~16 weeks, matching your existing DSA plan timeline
• Always redo Two Sum, Merge Intervals, Kth Largest, and Course Schedule cold — these 4 patterns cover a disproportionate share of actual interview questions
• Track weak patterns separately (yours: heaps, intervals) and over-index practice there