linkedlist: loop detect done

Author: Ram swaroop

src/me/ramswaroop/linkedlists/DetectLoop.java

@@ -0,0 +1,50 @@
+package me.ramswaroop.linkedlists;
+
+import me.ramswaroop.common.SingleLinkedList;
+import me.ramswaroop.common.SingleLinkedNode;
+
+/**
+ * Created by IntelliJ IDEA.
+ *
+ * @author: ramswaroop
+ * @date: 6/19/15
+ * @time: 9:24 AM
+ */
+public class DetectLoop<E> extends SingleLinkedList<E> {
+
+    /**
+     * Uses Flyod's Cycle Finding algorithm.
+     * <p/>
+     * This is the fastest method. Traverse
+     * linked list using two pointers. Move one
+     * pointer by one and other pointer by two.
+     * If these pointers meet at some node then
+     * there is a loop. If pointers do not meet
+     * then linked list does not have loop.
+     *
+     * @param node
+     * @return
+     */
+    public boolean isLoopPresent(SingleLinkedNode<E> node) {
+        SingleLinkedNode<E> prev = node, curr = node;
+        while (curr != null && curr.next != null) {
+            prev = prev.next;
+            curr = curr.next.next;
+            if (prev == curr) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    public static void main(String a[]) {
+        DetectLoop<Integer> linkedList = new DetectLoop<>();
+        linkedList.add(11);
+        linkedList.add(22);
+        linkedList.add(33);
+        linkedList.add(44);
+        linkedList.add(55);
+        linkedList.getNode(4).next = linkedList.getNode(3);
+        System.out.println(linkedList.isLoopPresent(linkedList.getNode(0)));
+    }
+}