ARRAYS & STRINGS – PROBLEM LIST
Here is a curated, leveled problem list for MODULE 1: ARRAYS & STRINGS
Designed for progressive learning → Beginner → Intermediate → Advanced
Includes LeetCode (LC), GeeksforGeeks (GFG), Codeforces (CF), and InterviewBit (IB) links.
MODULE 1: ARRAYS & STRINGS – PROBLEM LIST
| # | Problem Name | Platform | Difficulty | Key Technique | Link |
|---|---|---|---|---|---|
| 1 | Two Sum | LC | Easy | Hash Map | LC 1 |
| 2 | Best Time to Buy and Sell Stock | LC | Easy | One-pass (min so far) | LC 121 |
| 3 | Contains Duplicate | LC | Easy | Set / Sorting | LC 217 |
| 4 | Move Zeroes | LC | Easy | Two Pointers (in-place) | LC 283 |
| 5 | Rotate Array | LC | Easy | Reverse trick / Juggling | LC 189 |
| 6 | Maximum Subarray (Kadane) | LC | Medium | DP (optimized) | LC 53 |
| 7 | Merge Sorted Array | LC | Easy | Two pointers from end | LC 88 |
| 8 | Remove Duplicates from Sorted Array | LC | Easy | Two pointers | LC 26 |
| 9 | Trapping Rain Water | LC | Hard | Two pointers / Precompute | LC 42 |
| 10 | 3Sum | LC | Medium | Sort + Two Pointers | LC 15 |
| 11 | Container With Most Water | LC | Medium | Two pointers (greedy) | LC 11 |
| 12 | Longest Substring Without Repeating Characters | LC | Medium | Sliding Window + Set/Map | LC 3 |
| 13 | Longest Palindromic Substring | LC | Medium | Expand around center / DP | LC 5 |
| 14 | Merge Intervals | LC | Medium | Sort + Merge | LC 56 |
| 15 | Sort Colors (0,1,2) | LC | Medium | Dutch National Flag (3 pointers) | LC 75 |
| 16 | Subarray Sum Equals K | LC | Medium | Prefix Sum + Hash Map | LC 560 |
| 17 | Minimum Size Subarray Sum | LC | Medium | Sliding Window | LC 209 |
| 18 | Product of Array Except Self | LC | Medium | Prefix & Suffix Product | LC 238 |
| 19 | Find the Duplicate Number | LC | Medium | Floyd’s Cycle / Binary Search | LC 287 |
| 20 | Spiral Matrix | LC | Medium | Layer-by-layer simulation | LC 54 |
BONUS: STRING-SPECIFIC PROBLEMS
| # | Problem | Platform | Technique | Link |
|---|---|---|---|---|
| B1 | Valid Anagram | LC | Hash Map / Sorting | LC 242 |
| B2 | Longest Common Prefix | LC | Vertical scan / Trie | LC 14 |
| B3 | Implement strStr() (KMP) | LC | KMP / Sliding | LC 28 |
| B4 | Ransom Note | LC | Hash Map | LC 383 |
| B5 | Group Anagrams | LC | Hash Map with sorted key | LC 49 |
PRACTICE PLAN (4 Weeks)
| Week | Focus | Problems |
|---|---|---|
| 1 | Basics + Two Pointers | 1–8 |
| 2 | Sliding Window + Prefix | 9–13, 16–17 |
| 3 | Advanced Two Pointers | 10, 11, 14, 15, 18 |
| 4 | Hard + Strings | 19, 20, B1–B5 |
TIPS
- Solve in order → build intuition.
- Re-solve without hints after 3 days.
- Time yourself: Easy < 10 min, Medium < 20 min.
- Write clean code → use meaningful variable names.
- Dry run on small test cases.
Want this as a printable PDF or Notion table?
Or need solutions + explanations for any problem? Just ask!