Decode Ways
Detailed guide and Python implementation for the 'Decode Ways' problem.
Problem Statement
A message containing letters from A-Z can be encoded into numbers using the following mapping:
'A' -> "1"
'B' -> "2"
...
'Z' -> "26"
To decode an encoded message, all the digits must be grouped then mapped back into letters using the reverse mapping above. For example, "11106" can be mapped into:
- "AAJF" with the grouping (1 1 10 6)
- "KJF" with the grouping (11 10 6)
Note that the grouping (1 11 06) is invalid because "06" cannot be mapped into 'F' since "6" is different from "06".
Given a string s containing only digits, return the number of ways to decode it.
Write a function numDecodings(s: str) -> int.
- •1 <= len(s) <= 100
- •s contains only digits and may contain leading zero(s)
Examples
s = "12"
2
"12" could be decoded as "AB" (1 2) or "L" (12).
s = "226"
3
"226" could be decoded as "BZ" (2 26), "VF" (22 6), or "BBF" (2 2 6).
s = "06"
0
"06" cannot be mapped to 'F' because of the leading zero.
Need a Hint?
Edge Cases to Watch
- Empty input structures
- Single element inputs
- Large numerical bounds
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