LinkedList Cycle Detection

src/main/kotlin/Main.kt

@@ -1,5 +1,7 @@
 package main.kotlin
 
+import main.kotlin.dsalgoleetcode.LinkedListCycleDetection
+import main.kotlin.dsalgoleetcode.ListNode
 import main.kotlin.dsalgoleetcode.LongestSubstring
 import main.kotlin.dsalgoleetcode.TwoSum
 
@@ -11,11 +13,21 @@ fun main() {
     // Calling Two Sum class
     val twoSum = TwoSum()
     val result = twoSum.twoSum(nums = intArrayOf(1, 2, 3, 4, 5), target = 9)
+    println("Indices: ${result.joinToString(",")}")
 
     // Calling Longest Substring
     val longestSubstring = LongestSubstring()
     val lsResult = longestSubstring.lengthOfLongestSubstring(s = "abcabcbbb")
-
-    println("Indices: ${result.joinToString(",")}")
     println("Longest Substring : $lsResult")
+
+    // Calling LinkedList Cycle Detection
+    val linkedListCycleDetection = LinkedListCycleDetection()
+    val node1 = ListNode(1)
+    val node2 = ListNode(2)
+    val node3 = ListNode(3)
+    node1.next = node2
+    node2.next = node3
+    node3.next = node1 // cycle back to x
+    val llcdResult = linkedListCycleDetection.hasCycle(node1)
+    println("Has cycle $llcdResult")
 }

src/main/kotlin/dsalgoleetcode/LinkedListCycleDetection.kt

@@ -0,0 +1,48 @@
+package main.kotlin.dsalgoleetcode
+
+/**
+ * Linked List Cycle
+ *
+ * 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.
+ *
+ * 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).
+ * */
+
+class LinkedListCycleDetection {
+
+    /**
+     * Example:
+     * var li = ListNode(5)
+     * var v = li.`val`
+     * Definition for singly-linked list.
+     * class ListNode(var `val`: Int) {
+     *     var next: ListNode? = null
+     * }
+     */
+
+    fun hasCycle(head: ListNode?): Boolean {
+        var slow = head
+        var fast = head
+        while (fast != null && fast.next != null) {
+            slow = slow?.next
+            fast = fast.next?.next
+            if (slow == fast)
+                return true
+        }
+        return false
+    }
+}
+
+
+class ListNode(var `val`: Int) {
+    var next: ListNode? = null
+}