dsa · easy

Reverse String II

Given lowercase string s and a positive integer k, process s in windows of length 2k from the left:

• in each full window, reverse the first k characters and leave the next k characters as they are
• if the leftover tail has fewer than k characters, reverse the whole tail
• if the leftover tail has at least k but fewer than 2k characters, reverse the first k of the tail and leave the rest

Return the resulting string.

Example

s = "abcdefgh", k = 3. Windows are length 2k = 6, so the split is "abcdef" plus tail "gh".

In "abcdef" reverse the first 3: "cba" + "def". The tail "gh" has length 2, which is less than k, so reverse all of it: "hg".

Result: "cbadefhg".

s = "abcd", k = 2: one window of length 4. Reverse the first 2, leave the last 2 → "bacd".

## Arguments - s — lowercase string to rewrite - k — window half-width; reverse the first k of every 2k characters

Constraints

1 <= s.length <= 4*10^4 s consists of lowercase English letters 1 <= k <= 10^4 Hidden tests include near-max size for this bound; a slower-than-intended solution TLEs.

Examples

Example 1

Input:
"abcdefgh"
3

Expected:
cbadefhg

Example 2

Input:
"abcd"
2

Expected:
bacd

Example 3

Input:
"abcdefg"
2

Expected:
bacdfeg

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