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541, Reverse String II

MikeNovember 18, 2023Less than 1 minutestringeasystringtwo pointers

I Problem

Given a string s and an integer k, reverse the first k characters for every 2k characters counting from the start of the string.

Example 1
Input: s = "abcdefg", k = 2
Output: "bacdfeg"

Example 2
Input: s = "abcd", k = 2
Output: "bacd"

Constraints

Related Topics

II Solution

Approach 1: Two Pointers

pub fn reverse_str(s: String, k: i32) -> String {
    let k = k as usize;
    let len = s.len();
    let p = unsafe { s.as_bytes_mut() };
    let mut begin = 0_usize;
    let mut end = begin + k;

    loop {
        if begin >= len {
            break;
        }
        if end > len {
            end = len;
        }

        let mut l = begin;
        let mut r = end - 1;
        while l < r {
            p.swap(l, r);
            l += 1;
            r -= 1;
        }

        begin += 2 * k;
        end = begin + k;
    }

    s
}