String DP

1. Introduction to String DP

Sequences, alignment, transformation

2. When to Use String DP

Two strings → dp[i][j]

3. Problem - Regex Matching

LC 10 - dot and star patterns

4. Regex Matching - Why Naive Fails

Star means zero or more of previous

5. Regex Matching - Defining the DP

dp[i][j] = does prefix match?

6. Regex Matching - Transition

Zero times or extend match

7. Regex Matching - Base Cases

Empty vs patterns like a*b*

8. Regex Matching - Implementation

Handle *, then .

9. Regex Matching - Time and Space

O(mn) both time and space

10. Regex Matching - Edge Cases

.* matches everything

11. Lessons from Regex Matching

Operators create branches

12. Problem - Interleaving String

LC 97 - merge two strings

13. Interleaving String - Why DP?

14. Interleaving String - Solution

dp[i][j] uses s3[i+j-1]

15. Interleaving String - Building the State

16. Problem - Palindrome Partitioning

LC 131 - all palindrome partitions

17. Palindrome Partitioning - Solution

Precompute isPalin[i][j]

18. Palindrome Partitioning - Precomputation

Interval DP for palindrome check

19. SCS - Solution

SCS = len1 + len2 - LCS

20. SCS - Reconstruction

Backtrack through LCS table

21. Problem - Longest Palindromic Substring

LC 5 - longest palindrome substring

22. Longest Palindromic Substring - Solution

Expand around center or DP

23. Problem - Word Break

LC 139 - dictionary segmentation

24. Word Break - Solution

dp[i] = prefix can be split?

25. Quiz: String DP Patterns

Which pattern is this?

26. Quiz: String DP Edge Cases

Empty string, single char

27. Common Mistakes in String DP

1-indexed DP, 0-indexed strings

28. Problem - Scramble String

LC 87

29. Scramble String - Implementation

Solution approach

30. Problem - Count Different Palindromic Subsequences

LC 730

31. Count Different Palindromic Subsequences - Implementation

Solution approach

32. Problem - Distinct Subsequences II

LC 940

33. Distinct Subsequences II - Implementation

Solution approach

34. Problem - Palindrome Partitioning III

LC 1278

35. Palindrome Partitioning III - Implementation

Solution approach

36. Problem - Number of Ways to Form Target String

LC 1639

37. Number of Ways to Form Target String - Implementation

Solution approach

38. Section Recap

From edit distance to word break