Remove all adjacent duplicates in string ii

String Stack

60.9% acceptance

Feb 25, 2026

6063

124

You are given a string s and an integer k, a k duplicate removal consists of choosing k adjacent and equal letters from s and removing them, causing the left and the right side of the deleted substring to concatenate together. We repeatedly make k duplicate removals on s until we no longer can. Return the final string after all such duplicate removals have been made. It is guaranteed that the answer is unique.

Solution

Rust

Time O(n²)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn remove_duplicates(s: String, k: i32) -> String {
    let k = k as usize;
    // stack stores (char, count)
    let mut stack: Vec<(char, usize)> = Vec::new();
    for c in s.chars() {
      if let Some(last) = stack.last_mut() {
        if last.0 == c {
          last.1 += 1;
          if last.1 == k {
            stack.pop();
          }
          continue;
        }
      }
      stack.push((c, 1));
    }
    let mut result = String::new();
    for (c, cnt) in stack {
      for _ in 0..cnt {
        result.push(c);
      }
    }
    result
  }
}