solve

Author: sonjh1217

linked-list-cycle/sonjh1217.swift

@@ -0,0 +1,63 @@
+/**
+ * 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
+ *     }
+ * }
+ */
+
+extension ListNode: Equatable {
+    public static func == (lhs: ListNode, rhs: ListNode) -> Bool {
+        return lhs === rhs
+    }
+}
+
+extension ListNode: Hashable {
+    public func hash(into hasher: inout Hasher) {
+        hasher.combine(ObjectIdentifier(self))
+    }
+}
+
+class Solution {
+    // O(n) time / O(n) space
+    func hasCycle(_ head: ListNode?) -> Bool {
+        var visitedNodes = Set<ListNode>()
+        var node = head
+        
+        while node != nil {
+            guard let currentNode = node else {
+                return false
+            }
+            
+            if visitedNodes.contains(currentNode) {
+                return true
+            }
+            
+            visitedNodes.insert(currentNode)
+            node = currentNode.next
+        }
+        
+        return false
+    }
+    
+    // O(n) time / O(1) space
+    func hasCycleFloyd(_ 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
+    }
+}