AlgoSolveoRoadmap › Stage 9: Greedy & Dynamic Programming › Pattern 45 of 53
DSA pattern guide
DP — Strings
Two strings compared: LCS, edit distance, subsequence counts.
Use it when
Two strings compared: LCS, edit distance, subsequence counts.
Key idea
dp[i][j] = answer for prefixes s[:i], t[:j]. Match: diagonal. Mismatch: best of the neighbours.
Practice problems, in order
- Longest Common SubsequenceMedium
- Longest Palindromic SubsequenceMedium
- Edit DistanceMedium
- Shortest Common SupersequenceMedium
- Minimum Insertions to Make PalindromeMedium
- Regular Expression MatchingHard
- Distinct SubsequencesHard
- Palindrome Partitioning IIHard
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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