LC#142 find first meet point in linkedlist cycle - medium problem

Author: NirmalSilwal

Leetcode/leetcodeTags/LinkedList/LinkedListCycleII142.java

@@ -0,0 +1,50 @@
+package LinkedList;
+
+public class LinkedListCycleII142 {
+
+	class ListNode {
+		int val;
+		ListNode next;
+
+		ListNode(int x) {
+			val = x;
+			next = null;
+		}
+	}
+
+	public ListNode detectCycle(ListNode head) {
+
+		if (head == null || head.next == null)
+			return null;
+
+		ListNode ptr1 = head;
+		ListNode ptr2 = detectCycle1(head);
+
+		if (ptr2 == null)
+			return null;
+
+		while (ptr1 != ptr2) {
+			ptr1 = ptr1.next;
+			ptr2 = ptr2.next;
+		}
+
+		return ptr1 == ptr2 ? ptr1 : null;
+	}
+
+	private static ListNode detectCycle1(ListNode head) {
+		if (head == null || head.next == null)
+			return null;
+
+		ListNode slow = head, fast = head;
+
+		while (fast != null && fast.next != null) {
+			slow = slow.next;
+			fast = fast.next.next;
+
+			if (slow == fast) {
+				return fast;
+			}
+		}
+		return null;
+	}
+}