题解 | #牛群的重新分组#

package main
import . "nc_tools"
/*
 * type ListNode struct{
 *   Val int
 *   Next *ListNode
 * }
 */

/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 * 
 * @param head ListNode类 
 * @param k int整型 
 * @return ListNode类
*/
func reverseKGroup( head *ListNode ,  k int ) *ListNode {
    // write code here
    dummy := &ListNode{-1, head}
    prev := dummy
    for head != nil {
        start := head
        end := head
        for i := 1; i < k && end != nil; i ++ {
            end = end.Next
        }
        if end == nil {
            break
        }
        next := end.Next
        for start != end {
            temp := start.Next
            start.Next = end.Next
            end.Next = start
            start = temp
        }
        prev.Next = end
        prev = head
        head = next
    }
    return dummy.Next
}