Created
March 13, 2018 17:49
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Reverse linked list nodes in groups of K length
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func reverseKGroup(_ head: ListNode?, _ k: Int) -> ListNode? { | |
var count = 0 | |
var current = head | |
var previous: ListNode? | |
var newHead: ListNode? | |
while current != nil { | |
count += 1 | |
current = current?.next | |
} | |
current = head | |
for _ in 0 ..< (count / k) { | |
let startOfGroup = reverseGroup(start: current, count: k) | |
if newHead == nil { | |
newHead = startOfGroup | |
} | |
previous?.next = startOfGroup | |
previous = current | |
current = current?.next | |
} | |
return newHead ?? head | |
} | |
func reverseGroup(start: ListNode?, count: Int) -> ListNode? { | |
var current = start | |
var previous: ListNode? | |
var next: ListNode? | |
for _ in 1...count { | |
next = current?.next | |
current?.next = previous | |
previous = current | |
current = next | |
} | |
start?.next = current | |
return previous | |
} | |
public class ListNode { | |
public var val: Int | |
public var next: ListNode? | |
public init(_ val: Int, next: ListNode? = nil) { | |
self.val = val | |
self.next = next | |
} | |
} | |
extension ListNode: CustomStringConvertible { | |
public var description: String { | |
let description = "\(val) -> " | |
if let next = next { | |
return description + next.description | |
} else { | |
return description + "nil" | |
} | |
} | |
} |
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