AlgoSolveoRoadmap › Stage 5: Recursion & Linked Lists › Pattern 22 of 53
DSA pattern guide
Recursion — Divide & Conquer
Split the input in halves, solve each, merge.
Use it when
Split the input in halves, solve each, merge.
Key idea
Solve the left and right halves independently, then combine. Typical cost is O(n log n).
Practice problems, in order
- Reverse Linked List (Recursive)Easy
- Merge 2 Sorted ListsEasy
- Generate All SubsetsMedium
- Target Sum / Count SubsequencesMedium
- Median of Two Sorted ArraysHard
How to practise this pattern
- Read the problem and look for the signal above before writing any code.
- Say the brute force out loud, with its time complexity, then ask what work it repeats.
- Apply the key idea and write the optimised version yourself.
- If you're stuck for more than 10 minutes, take one small hint, not the full solution.
- Move to the next problem only when you can explain why this pattern fits.
Stuck on one of these?
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