NFA structure
2D grid of states: (position, errors so far). Transitions for each char + insert + delete + replace.
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Determinization
Convert NFA to DFA. States explode, but Schulz-Mihov shows DFA has O(N·k) states for practical k.
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Dictionary search
Intersect Levenshtein automaton with dictionary trie. Enumerate all valid dictionary words in one traversal.
Complexity
Per candidate word: O(|W|). Dictionary of size D: O(|W| + matches).