g0101_0200.s0141_linked_list_cycle.Solution.swift Maven / Gradle / Ivy

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104 LeetCode algorithm problem solutions

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// #Easy #Top_100_Liked_Questions #Top_Interview_Questions #Hash_Table #Two_Pointers #Linked_List
// #Data_Structure_I_Day_7_Linked_List #Udemy_Linked_List #Big_O_Time_O(N)_Space_O(1)
// #2024_06_27_Time_21_ms_(98.35%)_Space_16_MB_(82.04%)

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public var val: Int
 *     public var next: ListNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.next = nil
 *     }
 * }
 */
class Solution {
    func hasCycle(_ head: ListNode?) -> Bool {

       var slow = head
       var fast = head

       while fast != nil && fast?.next != nil {
        slow = slow?.next
        fast = fast?.next?.next

        if slow === fast {
            return true
        }
       }
       return false 
    }
}