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20 articles
Master advanced string algorithms: KMP failure function for O(n) pattern matching, Z-algorithm for all prefix matches, Rabin-Karp rolling hash, and suffix arrays for substring queries.
Implement KMP string search: build the failure function (LPS array) in O(m) then search in O(n). Never re-examines matched characters unlike naive search.
The Z-algorithm computes Z[i] = length of the longest substring starting at i that matches a prefix of the string. O(n) time, elegant and powerful for pattern search.
Rabin-Karp uses a rolling polynomial hash to match patterns in O(n+m) expected time. The key is updating the hash in O(1) as the window slides.
Find the longest palindromic substring in O(n) using Manacher's algorithm. Expands palindromes using a mirror trick to avoid redundant work.
Precompute polynomial prefix hashes to compare any two substrings in O(1). Enables O(n log n) LCP computation and O(n) duplicate detection.
Build a suffix array in O(n log²n) using doubling sort. Enables O(m log n) substring search, longest common substring, and number of distinct substrings.
Find the longest common substring between two strings. DP approach O(nm), binary search + rolling hash O((n+m) log(n+m)).
Core string DP patterns: edit distance (Wagner-Fischer), longest common subsequence, interleaving strings, and regular expression matching.
Group anagrams, find anagram indices, and count anagram occurrences. Three approaches: sort key O(nk log k), frequency tuple O(nk), and sliding window O(n+k).
Comprehensive palindrome problem coverage: valid palindrome check, longest palindromic substring (three methods), count palindromic substrings, and palindrome partitioning.
Word Search I and II solved with DFS backtracking. Word Search II uses a Trie to prune the search space from O(N·4^L) per word to O(N·4^L) total for all words.
Design an encode/decode scheme for a list of strings. Length-prefix encoding (4-byte header per string) is collision-proof unlike delimiter-based approaches.
Add minimum characters to the front of a string to make it a palindrome. KMP trick: concatenate s + '#' + rev(s), find the LPS value at the last position.
Count the number of distinct substrings using the suffix array and LCP array. Total substrings minus sum of LCP values gives distinct count in O(n log n).
Implement run-length encoding, string compression in-place, and decode compressed strings. Tests two-pointer technique and string manipulation.
Advanced trie applications beyond basic insert/search: binary trie for XOR maximization, palindrome pairs detection, and stream search using Aho-Corasick automaton concept.
High-frequency string problems from Meta and Google interviews: valid parentheses, longest substring without repeating characters, zigzag conversion, and string to integer.
Aho-Corasick automaton matches all patterns simultaneously in O(n+m+z) where z is the number of matches. Builds failure links on a trie for efficient multi-pattern search.
Complete recap of all 20 string algorithm problems: pattern recognition guide, algorithm selection, and complexity reference.