One Edit Distance

MediumStringstwo pointers

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

Practice this as a mock interviewFree to start, no account needed

Problem

Given two strings s and t, decide whether they are **exactly one edit** apart. A single edit is one of: inserting one character anywhere, deleting one character, or replacing one character with a different character. Return true if exactly one edit transforms s into t, otherwise false. Two identical strings are zero edits apart, so they return false. Comparison is case-sensitive. Aim for O(n) time and O(1) extra space, where n is the length of the longer string.

Examples

Input: s = "ab", t = "acb"
Output: true
Insert `c` between `a` and `b` in `s` to get `t`.
Input: s = "cab", t = "ad"
Output: false
The lengths differ by one, but deleting any single character from `"cab"` never yields `"ad"`.
Input: s = "1203", t = "1213"
Output: true
Replace the `0` at index 2 with `1`.

Constraints

  • 0 <= s.length <= 10^4
  • 0 <= t.length <= 10^4
  • `s` and `t` consist of lowercase letters, uppercase letters, and digits

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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