Remove All Adjacent Duplicates in String II

MediumStackstack

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

You are given a string s of lowercase English letters and an integer k. A **k-removal** picks k adjacent, identical characters and deletes them, joining the pieces on either side. Keep performing k-removals until none is possible, then return the final string. The result is the same regardless of which removals are chosen first, so it is uniquely defined. It may be empty. Aim for O(n) time.

Examples

Input: s = "xyyyxxz", k = 3
Output: "z"
Removing "yyy" joins the x's into "xxxz"; removing "xxx" leaves "z".
Input: s = "aabbccd", k = 2
Output: "d"
Each of "aa", "bb" and "cc" is removed, leaving "d".

Constraints

  • 1 <= s.length <= 10^5
  • 2 <= k <= 10^4
  • `s` consists of lowercase English letters.

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.

More stack problems