Solve Two String Problems

The interview included two coding questions:

1. Exactly one edit apart

   Given two strings s and t, determine whether they are exactly one edit apart.

   An edit is one of the following operations applied once:

   • Insert a single character
   • Delete a single character
   • Replace a single character

   Return true if you can transform one string into the other using exactly one edit, and false otherwise.

   Example cases:

   • s = "ab", t = "acb" -> true
   • s = "cab", t = "ad" -> false
   • s = "1203", t = "1213" -> true
   • s = "abc", t = "abc" -> false

2. Validate a word abbreviation

   Given a word word and a string abbr, determine whether abbr is a valid abbreviation of word.

   Rules:

   • Letters in abbr must match the corresponding letters in word.
   • A positive integer in abbr means skipping that many characters in word.
   • Numbers cannot contain leading zeros.
   • The abbreviation is valid only if it consumes the entire word exactly.

   Example cases:

   • word = "internationalization", abbr = "i12iz4n" -> true
   • word = "apple", abbr = "a2e" -> false
   • word = "substitution", abbr = "s10n" -> true
   • word = "word", abbr = "w02d" -> false

Implement efficient solutions for both problems.

Part 1: Exactly One Edit Apart

Given two strings s and t, determine whether they are exactly one edit apart. One edit means performing exactly one of these operations once: insert a single character, delete a single character, or replace a single character. Return True only if one string can be transformed into the other using exactly one edit. If they are already equal, or if they need two or more edits, return False.

Constraints

• 0 <= len(s), len(t) <= 100000
• Strings may contain any characters.
• An efficient linear-time solution is expected.

Examples

Example 1

Input: ('ab', 'acb')
Output: True

Explanation: Insert 'c' into 'ab' to get 'acb'.

Example 2

Input: ('cab', 'ad')
Output: False

Explanation: More than one edit is required.

Hints

1. If the string lengths differ by more than 1, they cannot be exactly one edit apart.
2. Use two pointers to scan both strings. At the first mismatch, decide whether it represents a replacement or skipping one character in the longer string.

Part 2: Validate a Word Abbreviation

Given a word word and an abbreviation abbr, determine whether abbr is a valid abbreviation of word. Letters in abbr must match the corresponding letters in word. A positive integer in abbr means skipping that many characters in word. Numbers in the abbreviation cannot have leading zeros, and the abbreviation is valid only if it consumes the entire word exactly.

Constraints

• 0 <= len(word), len(abbr) <= 100000
• abbr contains only letters and digits.
• Numbers in abbr represent positive skip lengths and cannot contain leading zeros.

Examples

Example 1

Input: ('internationalization', 'i12iz4n')
Output: True

Explanation: The abbreviation matches the word by skipping the correct number of characters.

Example 2

Input: ('apple', 'a2e')
Output: False

Explanation: After matching 'a' and skipping 2 characters, the next letter should be 'l', not 'e'.

Hints

1. Walk through both strings with two pointers. When you see digits in abbr, parse the whole number before moving on.
2. A digit '0' cannot start a number in the abbreviation.