Coding Practice: Strings, Sliding Window, and Two Pointers

TL;DR

• Strings and windows are common because they reward precise state tracking.
• I practice them as parsing and UI-search problems, not just textbook substring exercises.
• The key move is defining exactly what makes the current window valid.

Context

Frontend work constantly touches strings: search boxes, route parsing, query handling, template variables, validation, and text transforms. Sliding window helps when I need contiguous ranges without nested loops.

The Approach

Practice these 10 medium-level questions:

1. Longest Substring Without Repeating Characters — canonical variable-window problem.
2. Minimum Window Substring — track deficits precisely.
3. Longest Repeating Character Replacement — balance window size with tolerated replacements.
4. Valid Palindrome II — allow one deletion with pointer branching.
5. Group Shifted Strings — normalize relative character offsets.
6. Find All Anagram Start Indices — fixed-size window frequency matching.
7. Compare Version Strings — parse segments without naive lexical compare.
8. Decode Encoded String — nested pattern parsing like 3[a2[c]].
9. Template Placeholder Expansion — replace tokens from a map with fallback handling.
10. Longest Common Prefix After Sorting — comparator plus prefix scan.

Try it in the browser

Trade-offs

• Sliding window is powerful, but only when the invariant is clear.
• Pointer-based solutions are fast, but they become fragile if I do not document what each boundary means.

References

• Related: Coding Practice: Arrays
• Related: Coding Practice: Searching