7 articles
LC 127 Word Ladder asks for the shortest sequence of one-letter transformations from beginWord to endWord, where every intermediate word must be in the dictionary. BFS on the implicit word-state graph finds the minimum in O(M^2 * N) using wildcard pattern grouping.
LC 819 Most Common Word finds the most frequent non-banned word in a paragraph using normalization, regex tokenization, and a frequency hash map — a practical string-processing problem tested at Amazon and Microsoft.
Remove adjacent pairs of same letters with different cases using a stack that processes each character and cancels bad pairs immediately. A clean application of the stack-based adjacent-pair-removal pattern common in FAANG string interviews.
Decode a run-length encoded string with nested brackets like 3[a2[bc]] using two stacks for counts and partial strings. A key FAANG problem testing nested structure parsing with stacks — the same pattern used in expression evaluators and compilers.
Solve LeetCode 127 Word Ladder using BFS with a queue and a wildcard pattern map for O(1) neighbor lookups. A FAANG hard at Amazon, Google, Meta, and Microsoft that tests BFS on implicit graphs.
Solve LeetCode 1209 Remove All Adjacent Duplicates II in O(n) using a counter stack of (char, count) pairs. A FAANG-favorite stack twist asked at Google and Amazon.
LeetCode 648 — replace each word in a sentence with the shortest dictionary root that prefixes it. The trie walks one character at a time, returning the first isEnd we hit. A clean autocomplete-style problem.