java: add «141. Linked List Cycle»

Signed-off-by: Matej Focko <mfocko@redhat.com>

java/linked-list-cycle.java

@@ -0,0 +1,21 @@
+/**
+ * Definition for singly-linked list. class ListNode { int val; ListNode next; ListNode(int x) { val
+ * = x; next = null; } }
+ */
+public class Solution {
+  public boolean hasCycle(ListNode head) {
+    var x = head;
+    var y = head;
+
+    while (y != null && y.next != null) {
+      x = x.next;
+      y = y.next.next;
+
+      if (x == y) {
+        return true;
+      }
+    }
+
+    return false;
+  }
+}