Decode Ways

Explore how to count the number of ways to decode a digit-only string into alphabetic characters. Understand the mapping rules from digits to letters and learn to apply dynamic programming to efficiently solve the problem. Practice implementing solutions considering valid and invalid encodings, as well as handling edge cases.

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Statement

Given a string that has only positive digits, your task is to decode the string and determine the number of possible ways to decode it.

Consider the input string as an encoded message, where each digit in the string represents an alphabet from A to Z. For reference, let’s look at the mapping below:

"1" represents "A"

"2" represents "B"

"3" represents "C"

$\dots$

"26" represents "Z"

How to perform the decode operation?

To decode an encoded message, we have to check whether or not each digit in the string can be mapped onto the mapping above. There can be multiple ways to decode a string.

For example, the string "231012" can be decoded in the following ways:

Option ...