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141LinkedListCycle.swift
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141LinkedListCycle.swift
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/*
Given head, the head of a linked list, determine if the linked list has a cycle in it.
There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally, pos is used to denote the index of the node that tail's next pointer is connected to. Note that pos is not passed as a parameter.
Return true if there is a cycle in the linked list. Otherwise, return false.
Example 1:
Input: head = [3,2,0,-4], pos = 1
Output: true
Explanation: There is a cycle in the linked list, where the tail connects to the 1st node (0-indexed).
Visualization - https://assets.leetcode.com/uploads/2018/12/07/circularlinkedlist.png
Example 2:
Input: head = [1,2], pos = 0
Output: true
Explanation: There is a cycle in the linked list, where the tail connects to the 0th node.
Visualization - https://assets.leetcode.com/uploads/2018/12/07/circularlinkedlist_test2.png
*/
struct Solution {
func hasCycle(_ head: ListNode?) -> Bool {
guard
head != nil,
head?.next != nil,
head?.next?.next != nil
else {
return false
}
var slowIterator = head
var fastIterator = head
while fastIterator?.next != nil && fastIterator?.next?.next != nil {
slowIterator = slowIterator?.next
fastIterator = fastIterator?.next?.next
if slowIterator === fastIterator {
return true
}
}
return false
}
}