Decode Ways
Intermediate
A message uses the code A = 1, B = 2, ..., Z = 26. Given a string s of digits, return the number of ways to decode it into letters (a digit group like "06" or "0" alone is not a valid code). The answer is returned modulo 10**9 + 7.
For "12" the answer is 2 (AB or L); for "226" it is 3; for "06" it is 0.
Examples
Example 1
Input:
num_decodings('12')
Output:
2
Example 2
Input:
num_decodings('226')
Output:
3
Example 3
Input:
num_decodings('06')
Output:
0
Constraints
0 <= len(s) <= 200000scontains only digits.
Theory
Go to TheoryKeywords
dsa-sheetdynamic-programmingsequences-and-counting
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