Decode Ways: coding question

Problem

A simple code changes a message of uppercase letters into a string of digits. Each letter becomes its position in the alphabet: A is 1, B is 2 and Z is 26.

The code writes these numbers one after the other. For example, the message "LAB" becomes "1212".

You get a string s of digits. Return the number of ways to decode s. To decode s, split it into parts so that each part is the number of one letter.

A part cannot start with 0. So "6" and "10" are valid parts, but "06" and "0" are not. If no split is valid, return 0.

Example 1

Input:: s = "123"
Output:: 3
Explanation:: The splits are 1 2 3, 12 3 and 1 23. They decode to "ABC", "LC" and "AW".

Example 2

Input:: s = "2101"
Output:: 1
Explanation:: The only valid split is 2 10 1. The 0 cannot be a part alone, so it must be the end of the part 10.

Example 3

Input:: s = "30"
Output:: 0
Explanation:: The number 30 is larger than 26, and 0 cannot be a part alone.

Constraints

1 <= s.length <= 100
s has only digits. It can start with 0.
The answer fits in a 32-bit integer.

SysRound wrote this statement. A reference solution checks every example.

Continue with questions that share topics or the same question type.

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Sources · 2 references

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Hello Interview · 2 records

Anduril
Leetcode 91. Decode Ways
Reported May 1, 2026 · 1 source report
SENIOR
Source snapshot: Nov 12, 2026
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Meta
Leetcode 91. Decode Ways
Reported Aug 22, 2024 · 1 source report
SENIOR
Source snapshot: Nov 12, 2026
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LeetCode company tags · 2 records

Anduril
Decode Ways
Reported date not specified · Source window: 6mo
Source snapshot: Oct 20, 2026
Source frequency score: 65.6. This is not an interview probability.
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Lyft
Decode Ways
Reported date not specified · Source window: 6mo
Source snapshot: Oct 20, 2026

Problem

A simple code changes a message of uppercase letters into a string of digits. Each letter becomes its position in the alphabet: A is 1, B is 2 and Z is 26.

The code writes these numbers one after the other. For example, the message "LAB" becomes "1212".

You get a string s of digits. Return the number of ways to decode s. To decode s, split it into parts so that each part is the number of one letter.

A part cannot start with 0. So "6" and "10" are valid parts, but "06" and "0" are not. If no split is valid, return 0.

Example 1

Input:: s = "123"
Output:: 3
Explanation:: The splits are 1 2 3, 12 3 and 1 23. They decode to "ABC", "LC" and "AW".

Example 2

Input:: s = "2101"
Output:: 1
Explanation:: The only valid split is 2 10 1. The 0 cannot be a part alone, so it must be the end of the part 10.

Example 3

Input:: s = "30"
Output:: 0
Explanation:: The number 30 is larger than 26, and 0 cannot be a part alone.

Constraints

1 <= s.length <= 100
s has only digits. It can start with 0.
The answer fits in a 32-bit integer.

SysRound wrote this statement. A reference solution checks every example.

Decode Ways

Problem

Example 1

Example 2

Example 3

Constraints

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Decode Ways

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