Reverse String II

Problem statement

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.

Example 1:

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

Example 2:

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

Constraints:

• 1 <= s.length <= 104
• s consists of only lowercase English letters.
• 1 <= k <= 104

My solution

/**
 * @param {string} s
 * @param {number} k
 * @return {string}
 */
var reverseStr = function(s, k) {
    let sArr = s.split("")
    let step = 2 * k;
    
    for (let i = 0; i < sArr.length; i += step) {
        sArr = reverse(sArr, i, k)
    }
    
    return sArr.join("")
};

function reverse(arr, start, length) {
    let end = Math.min(arr.length - 1, start + length - 1)
    while (start < end) {
        [arr[end], arr[start]] = [arr[start], arr[end]]
        start++
        end--
    }
    
    return arr
}