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 left the other as original. Example 1: Input: s = "abcdefg", k = 2 Output: "bacdfeg" Example 2: Input: s = "abcd", k = 2 Output: "bacd" Constraints: 1 <= s.length <= 104 s consists of only lowercase English letters. 1 <= k <= 104