diff --git a/src/main/java/com/cool/hot100/linkedlist/Node.java b/src/main/java/com/cool/hot100/linkedlist/Node.java
new file mode 100644
index 0000000..452fae1
--- /dev/null
+++ b/src/main/java/com/cool/hot100/linkedlist/Node.java
@@ -0,0 +1,20 @@
+package com.cool.hot100.linkedlist;
+
+/**
+ * Created with IntelliJ IDEA.
+ *
+ * @Author: Cool
+ * @Date: 2024/08/24/23:22
+ * @Description:
+ */
+public class Node {
+    int val;
+    Node next;
+    Node random;
+
+    public Node(int val) {
+        this.val = val;
+        this.next = null;
+        this.random = null;
+    }
+}
diff --git a/src/main/java/com/cool/hot100/linkedlist/Num138.java b/src/main/java/com/cool/hot100/linkedlist/Num138.java
new file mode 100644
index 0000000..9a0751f
--- /dev/null
+++ b/src/main/java/com/cool/hot100/linkedlist/Num138.java
@@ -0,0 +1,59 @@
+package com.cool.hot100.linkedlist;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Created with IntelliJ IDEA.
+ *
+ * @Author: Cool
+ * @Date: 2024/08/24/23:21
+ * DayNumber 1
+ * Hard 2
+ */
+public class Num138 {
+
+    Map<Node, Node> cacheMap = new HashMap<>();
+
+    public Node copyRandomList(Node head) {
+        //ans1
+//        head = copyNode(head);
+//        return head;
+        //ans2
+        if(head==null){
+            return null;
+        }
+        for (Node node=head;node!=null;node=node.next.next){
+            Node newNode = new Node(node.val);
+            newNode.next=node.next;
+            node.next=newNode;
+        }
+        for (Node node=head;node!=null;node=node.next.next){
+            Node newNode = node.next;
+            newNode.random= node.random==null?null:node.random.next;
+        }
+        Node newHead=head.next;
+        for(Node node=head;node!=null;node=node.next){
+            Node newNode=node.next;
+            node.next=node.next.next;
+            newNode.next=newNode.next==null?null:newNode.next.next;
+        }
+        return newHead;
+    }
+
+    private Node copyNode(Node node) {
+        if (node == null) {
+            return null;
+        }
+        if (cacheMap.containsKey(node)) {
+            node = cacheMap.get(node);
+            return node;
+        }
+        Node copyNode = new Node(node.val);
+        cacheMap.put(node, copyNode);
+        copyNode.next = copyNode(node.next);
+        copyNode.random = copyNode(node.random);
+        return copyNode;
+    }
+
+}
diff --git a/src/main/java/com/cool/one_question_per_day/LeetCode20240825.java b/src/main/java/com/cool/one_question_per_day/LeetCode20240825.java
new file mode 100644
index 0000000..d5d15b7
--- /dev/null
+++ b/src/main/java/com/cool/one_question_per_day/LeetCode20240825.java
@@ -0,0 +1,16 @@
+package com.cool.one_question_per_day;
+
+/**
+ * Created with IntelliJ IDEA.
+ *
+ * @Author: Cool
+ * @Date: 2024/08/25/1:43
+ * @Description:
+ */
+public class LeetCode20240825 {
+
+    public int findPermutationDifference(String s, String t) {
+
+    }
+
+}