solves linkedlist cycle ii in java

Author: anishLearnsToCode

Diff for: README.md

@@ -126,7 +126,7 @@
 | 138  | [Copy List with Random Pointer](https://leetcode.com/problems/copy-list-with-random-pointer)                                                              |                                                            [![Java](assets/java.png)](src/CopyListWithRandomPointer.java)                                                            |                                                                                                                                   |
 | 139  | [Word Break](https://leetcode.com/problems/word-break)                                                                                                    |                                                                    [![Java](assets/java.png)](src/WordBreak.java)                                                                    |                                                                                                                                   |
 | 141  | [Linked List Cycle](https://leetcode.com/problems/linked-list-cycle)                                                                                      |                                   [![Java](assets/java.png)](src/LinkedListCycle.java) [![Python](assets/python.png)](python/linked_list_cycle.py)                                   |                                                                                                                                   |
-| 142  | [Linked List Cycle II](https://leetcode.com/problems/linked-list-cycle-ii)                                                                                |                                                                                                                                                                                      |                                                                                                                                   |
+| 142  | [Linked List Cycle II](https://leetcode.com/problems/linked-list-cycle-ii)                                                                                |                                                                [![Java](assets/java.png)](src/LinkedListCycleII.java)                                                                |                                                                                                                                   |
 | 143  | [Reorder List](https://leetcode.com/problems/reorder-list)                                                                                                |                                                                                                                                                                                      |                                                                                                                                   |
 | 144  | [Binary Tree Preorder Traversal](https://leetcode.com/problems/binary-tree-preorder-traversal)                                                            |                      [![Java](assets/java.png)](src/BinaryTreePreOrderTraversal.java) [![Python](assets/python.png)](python/binary_tree_preorder_traversal.py)                       |                                                                                                                                   |
 | 145  | [Binary Tree Postorder Traversal](https://leetcode.com/problems/binary-tree-postorder-traversal)                                                          |                     [![Java](assets/java.png)](src/BinaryTreePostorderTraversal.java) [![Python](assets/python.png)](python/binary_tree_postorder_traversal.py)                      |                                                                                                                                   |

Diff for: src/LinkedListCycleII.java

@@ -0,0 +1,24 @@
+// https://leetcode.com/problems/linked-list-cycle-ii
+// T: O(n)
+// S: O(1)
+
+public class LinkedListCycleII {
+    public ListNode detectCycle(ListNode head) {
+        if (head == null) return null;
+
+        ListNode slow = head, fast = head, entry = head;
+        while (fast.next != null && fast.next.next != null) {
+            slow = slow.next;
+            fast = fast.next.next;
+
+            if (slow == fast) {
+                while (entry != slow) {
+                    entry = entry.next;
+                    slow = slow.next;
+                }
+                return entry;
+            }
+        }
+        return null;
+    }
+}