Reverse string ii

Two Pointers String

53.4% acceptance

Feb 19, 2026

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Given a string s and an integer k, reverse the first k characters for every 2k characters counting from the start of the string. If there are fewer than k characters left, reverse all of them. If there are less than 2k but greater than or equal to k characters, then reverse the first k characters and leave the other as original.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn reverse_str(s: String, k: i32) -> String {
    let k = k as usize;
    let mut chars: Vec<char> = s.chars().collect();
    let n = chars.len();
    let mut i = 0;
    while i < n {
      let end = (i + k).min(n);
      chars[i..end].reverse();
      i += 2 * k;
    }
    chars.iter().collect()
  }
}