添加 0142.环形链表II.md Java版本

problems/0142.环形链表II.md

@@ -186,7 +186,35 @@ public:
 
 
 Java：
+```java
+public class Solution {
+    public ListNode detectCycle(ListNode head) {
+        // 1.寻找相遇点
+        ListNode fast = head;
+        ListNode slow = head;
 
+        while (fast != null && fast.next != null) {
+            fast = fast.next.next;
+            slow = slow.next;
+            if (fast != slow) {
+                continue;
+            }
+            ListNode meet = fast;
+
+            // 2.寻找入口点
+            slow = head;
+            while (slow != fast) {
+                slow = slow.next;
+                fast = fast.next;
+            }
+
+            return fast;
+        }
+
+        return null;
+    }
+}
+```
 
 Python：