strings Mastery
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Topic Cheat Sheet
Pattern Matching
- KMP AlgorithmLPS array, O(n+m) substring search
- Rabin-KarpRolling hash, O(n+m) avg, good for multiple patterns
- Z-AlgorithmZ-array for pattern occurrences in O(n+m)
Two Pointers / Sliding Window
- Palindrome Checkleft/right pointers moving inward
- Longest Substring (No Repeat)Sliding window + HashSet
- Minimum Window SubstringExpand right, shrink left, freq map
- Anagram DetectionFixed-size window + char frequency
HashMap / Frequency
- Valid Anagramint[26] freq count comparison
- Group AnagramsSorted string as key → HashMap grouping
- First Unique CharFrequency array + single pass
- Ransom NoteFreq count of available chars
DP & Stack
- Longest Palindromic SubstringExpand around center or dp[i][j]
- Edit DistanceInsert/delete/replace, dp[i][j]
- Valid ParenthesesStack: push open, pop on close
- Decode StringStack of [string, count] pairs
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