linked list cycle

Author: eunhwa99

linked-list-cycle/eunhwa99.java

@@ -0,0 +1,36 @@
+
+class ListNode {
+
+  int val;
+  ListNode next;
+
+  ListNode(int x) {
+    val = x;
+    next = null;
+  }
+}
+
+public class Solution {
+
+  // Floyd's Tortoise and Hare Algorithm
+  // TC: O(N)
+  // SC: O(1)
+  public boolean hasCycle(ListNode head) {
+    if (head == null || head.next == null) {
+      return false;
+    }
+
+    ListNode slow = head;
+    ListNode fast = head;
+
+    while (fast != null && fast.next != null) {
+      slow = slow.next;
+      fast = fast.next.next;
+
+      if (slow == fast) {
+        return true;
+      }
+    }
+    return false;
+  }
+}