415. Reverse Every Alternate Group of K Nodes

Given a linked list and an integer k, reverse the first group of k nodes, leave the next group of k as-is, reverse the following group, and so on alternately (the first group is reversed). A final partial group follows the same alternating rule. Return the result as an array. Input: '[list], k'.

Input: '[list], k'.

Output: Array — the modified list.

Examples

Input: [1,2,3,4,5,6,7,8,9], 3
Output: [3,2,1,4,5,6,9,8,7]
Explanation: Reverse, keep, reverse.

Input: [1,2,3,4,5], 2
Output: [2,1,3,4,5]
Explanation: Reverse first pair, keep next.

Input: [1], 1
Output: [1]
Explanation: Single node reversed (itself).

Constraints

• 0<=n<=10^4
• 1<=k<=n

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