Phone Keypad Problem

Solve a problem based on Recursion and Backtracking.

Problem statement

Before the advent of QWERTY keyboards, texts and numbers were placed on the same key. For example, 2 had ABC and if we wanted to write anything starting with A, we needed to type key 2 once. If we wanted to type B, key 2 had to be pressed twice, and thrice for typing C. Below is a picture of such a keypad.

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