Reverse String II

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, reverse the first k characters and leave the other characters as original.

Example 1

Inputs = "abcdefg", k = 2

Output"bacdfeg"

For every 2k = 4 characters, the first 2 characters are reversed, producing "bacdfeg".

Example 2

Inputs = "abcd", k = 2

Output"bacd"

The first 2 characters are reversed and the remaining characters are left unchanged.

Constraints