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ReverseLinkedListIIMedium92.swift
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ReverseLinkedListIIMedium92.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 reverseBetween(_ head: ListNode?, _ left: Int, _ right: Int) -> ListNode? {
let dummy = ListNode(0)
dummy.next = head
var prev: ListNode? = dummy
var node: ListNode? = head
var index = 1
while index < left && node != nil {
prev = node
node = node!.next
index += 1
}
let leftTail: ListNode! = prev
let rightHead: ListNode? = node
var next: ListNode?
while index <= right && node != nil {
next = node!.next
node!.next = prev
prev = node
node = next
index += 1
}
leftTail.next = prev
rightHead?.next = node
return dummy.next
}
}
//let five = ListNode(5)
//let four = ListNode(4, five)
//let three = ListNode(3, four)
//let two = ListNode(2, three)
//let one = ListNode(1, two)
//Solution().reverseBetween(one, 2, 4)