Meta Software Developer interview questions

Given a mapping of Char to Char array. Given an input string S. Find all possible strings that can be generated. every character in the input string should be replaced by a character in its corresponding mapped array of characters. Ex: '1' => ['a', 'b', 'c'] '2' => ['d', 'e'] . . . Input : "12" output: ["ad", "ae", "bd", "be", "cd", "ce"]