Reverse_String_II.js

/*
Reverse String II
https://leetcode.com/problems/reverse-string-ii/description/

Given a string and an integer k, you need to reverse the first k characters for every 2k characters counting from the start of the string. If there are less 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 left the other as original.
Example:
Input: s = "abcdefg", k = 2
Output: "bacdfeg"
Restrictions:
The string consists of lower English letters only.
Length of the given string and k will in the range [1, 10000]
*/

var reverseStr = function (s, k) {
  if (k <= 1) return s;
  var ret = "";
  for (var iterK = 0; iterK * k < s.length; iterK = iterK + 2) {
    const start = iterK * k;
    const end = start + k - 1;

    ret += reverse(s, start, end);
    ret += s.slice(end + 1, k * (iterK + 2));
  }

  return ret;
};

var reverse = function (s, start, end) {
  var ret = "";
  if (end >= s.length) end = s.length - 1;

  while (start <= end) {
    ret += s.charAt(end);
    end--;
  }
  return ret;
};

module.exports.reverseStr = reverseStr;