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0025_Reverse_Nodes_in_k-Group.swift
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0025_Reverse_Nodes_in_k-Group.swift
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/**
* Definition for singly-linked list.
* public class ListNode {
* public var val: Int
* public var next: ListNode?
* public init() { self.val = 0; self.next = nil; }
* public init(_ val: Int) { self.val = val; self.next = nil; }
* public init(_ val: Int, _ next: ListNode?) { self.val = val; self.next = next; }
* }
*/
class Solution {
func reverseKGroup(_ head: ListNode?, _ k: Int) -> ListNode? {
var start: ListNode? = head
for _ in 0 ..< k - 1 {
start = start?.next
}
if start == nil {
return head
} else {
var current: ListNode?
var tmp: ListNode?
for _ in 0..<k {
if current == nil {
current = head?.next
head?.next = reverseKGroup(start?.next, k)
start = head
} else {
tmp = current?.next
current?.next = start
start = current
current = tmp
}
}
return start
}
}
}