Tries & Prefix Search

Segmentation is the exception to Bloomberg's light dynamic programming, and the yes-or-no version is rarely the end of it. One form wants the sentence rebuilt with spaces. The harder one wants every sentence the string can become. The prefix tree is here because both problems work over a dictionary. Bloomberg asks typeahead as a system design, and it also asks for the trie itself in code, as prefix completion over a list of words. A hash set only tells you whether one exact string is a word. A trie tells you which words begin at a given point, in one pass down the tree, and that speeds up the segmentation too. Get the memoised or tabulated segmentation passing first. A working memo with time left beats a half-built trie when the clock runs out. While you fill the table, record which word you took at each position, so rebuilding the sentence is one walk from the front.

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