dsa · medium
Decode Ways
A message of letters A-Z is encoded as 1 → A, 2 → B, …, 26 → Z. Given a string s of digits, return how many ways it can be decoded. A leading zero cannot start a code ("06" is 0 ways).
Arguments
s— digit string; count decodings into A-Z via 1..26
Example
"12" → 2 (AB = 1,2 or L = 12).
"226" → 3 (BZ 2,26 / VF 22,6 / BBF 2,2,6).
"06" → 0.
Constraints
1 <= s.length <= 100 s contains only digits and may contain leading zeros Hidden tests include near-max size for this bound; a slower-than-intended solution TLEs.
Examples
Example 1
Input: "12" Expected: 2
Example 2
Input: "226" Expected: 3
Example 3
Input: "06" Expected: 0