linked list cycle

Author: GouravRusiya30

Java/linked-list.java

@@ -0,0 +1,45 @@
+/**
+ * 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) {
+ 
+ if (head == null){
+ return false;
+ }
+ 
+ ListNode slowPtr = head;
+ ListNode fastPtr = head;
+ 
+ /** Approach
+ 
+ // 1. if no cycle exists AND
+ // a. if there are even number of nodes then fast pointer will be pointing to null.
+ // b. else there are odd number of nodes then fast pointer will be pointing to last node.
+ 
+ // 2. if slow pointer meet fast pointer that interprets there exists a loop 
+ */
+ 
+ while (fastPtr != null && fastPtr.next != null) {
+ 
+ // move slow pointer one node at a time
+ slowPtr = slowPtr.next;
+ 
+ // move fast pointer two nodes at a time
+ fastPtr = fastPtr.next.next;
+ 
+ if (slowPtr == fastPtr)
+ return true;
+ }
+ 
+ return false;
+ }
+}