LeetCode #17: Letter Combinations of a Phone Number — Solved in Java

Backtracking with Basic Map and Prebuilt Lookup and Iterative Queue

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This problem takes a string of digits and asks you to figure out all the possible letter groupings those digits could make based on a classic phone keypad. Each number from 2 through 9 maps to a set of letters, and the goal is to build every combination you can by picking one letter for each digit, in order.

At first, it helps to think of the…