Phone Keypad problem using recursion

#1

what would be time complexity in this case?

#2

Time Complexity: O(4^n), where n is number of digits in input number.
Each digit of a number has 3 or 4 alphabets, so it can be said that each digit has 4 alphabets as options. If there are n digits then there are 4 options for first digit and for each alphabet of first digit there are 4 options in second digit, i.e for every recursion 4 more recursion is called (if it does not match the base case). So the time complexity is O(4^n).

#3

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