Check Whether a Letters-and-Numbers Abbreviation Matches a Word
Company: Meta
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Technical Screen
A word can be abbreviated by replacing some of its non-empty substrings with their lengths, written in decimal. For example, `"abbreviation"` can be written as `"a10n"`, `"ab3v2t1on"` or `"12"`.
Given a string `word` and a string `abbr`, return whether `abbr` is a valid abbreviation of `word`.
### Function Signature
```python
def is_valid_abbreviation(word: str, abbr: str) -> bool:
```
### Rules
- Read `abbr` from left to right. A letter must equal the next unmatched character of `word`. A maximal run of consecutive digits is read as one decimal number `k`, and it skips the next `k` characters of `word`.
- A digit run that starts with `0` is invalid, so runs such as `"0"` or `"05"` never appear in a valid abbreviation. Every skip is therefore at least 1 character.
- `abbr` is valid exactly when the end of `abbr` and the end of `word` are reached at the same time. A skip that would go past the end of `word` makes `abbr` invalid, and so does reaching the end of `abbr` while characters of `word` remain.
- Letters are compared exactly.
### Constraints
- `1 <= len(word) <= 10^5`, and `word` consists of lowercase English letters.
- `1 <= len(abbr) <= 10^5`, and `abbr` consists of lowercase English letters and the digits `0` to `9`.
- Every maximal run of digits in `abbr` has at most 9 digits, so every skip count is below `10^9` and fits in a 32-bit signed integer.
### Examples
**Example 1**
```text
Input: word = "abbreviation", abbr = "ab3v2t1on"
Output: True
```
`"ab"` matches, `3` skips `"bre"`, `"v"` matches, `2` skips `"ia"`, `"t"` matches, `1` skips `"i"`, and `"on"` matches. Both strings end together.
**Example 2**
```text
Input: word = "substitution", abbr = "s010n"
Output: False
```
The digit run `"010"` starts with `0`.
**Example 3**
```text
Input: word = "apple", abbr = "a2e"
Output: False
```
After `"a"` matches and `2` skips `"pp"`, the next character of `word` is `"l"`, which does not equal `"e"`.
Overview: Decide whether an abbreviation made of lowercase letters and decimal skip counts matches a given word, where each number skips that many characters and any number with a leading zero is invalid. It tests careful string scanning, multi-digit number parsing and end-of-input boundary checks.