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.
Input: s = "abcdefg", k = 2 Output: "bacdfeg"
Input: s = "abcd", k = 2 Output: "bacd"
1 <= s.length <= 104
sconsists of only lowercase English letters.
1 <= k <= 104