141

suke · suke · commit 99cec1cd8f98 · 2019-05-07T10:52:11.000+08:00
diff --git a/Week_01/id_121/LeetCode_141_121.java b/Week_01/id_121/LeetCode_141_121.java
@@ -0,0 +1,42 @@
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) {
+ *         val = x;
+ *         next = null;
+ *     }
+ * }
+ */
+public class Solution {
+    public ListNode detectCycle(ListNode head) {
+        ListNode fast = head;
+        ListNode slow = head;
+        ListNode meet = null;
+
+        while(fast != null){
+            fast = fast.next;
+            slow = slow.next;
+            if(fast == null){
+                return null;
+            }
+
+            fast = fast.next;
+            if(fast == slow){
+                meet = fast;
+                break;
+            }
+        }
+        while(meet != null && head != null){
+            if(meet == head){
+                return meet;
+            }
+            meet = meet.next;
+            head = head.next;
+        }
+        return null;
+
+
+    }
+}
