diff --git a/src/leo/class02_03/LinkedList.java b/src/leo/class02_03/LinkedList.java
index 44f1b09..40cd5fc 100644
--- a/src/leo/class02_03/LinkedList.java
+++ b/src/leo/class02_03/LinkedList.java
@@ -169,7 +169,7 @@ public class LinkedList {
         if (head == null) {
             return null;
         }
-        Node pre = head;
+        Node pre = null;
         Node next = null;
         while (head != null) {
             next  = head.next;
@@ -180,6 +180,21 @@ public class LinkedList {
         return pre;
     }
 
+    public static Node reverseNode11(Node head) {
+        if (head == null || head.next == null) {
+            return head;
+        }
+        Node pre = null;
+        Node next = null;
+        while (head != null) {
+            next = head.next;
+            head.next = pre;
+            pre = head;
+            head = next;
+        }
+        return pre;
+    }
+
     public static DoubleNode reverseDoubleNode(DoubleNode head) {
         DoubleNode pre = null;
         DoubleNode next;
@@ -263,7 +278,7 @@ public class LinkedList {
         if (head == null) {
             return null;
         }
-        DoubleNode pre = head;
+        DoubleNode pre = null;
         DoubleNode next = null;
         while (head != null) {
             next = head.next;
@@ -276,6 +291,23 @@ public class LinkedList {
 
     }
 
+
+    public static DoubleNode reverseDoubleNode7(DoubleNode head){
+        if (head == null || head.next == null) {
+            return head;
+        }
+        DoubleNode pre = null;
+        DoubleNode next = null;
+        while (head != null) {
+            next = head.next;
+            head.pre = head.next;
+            head.next = pre;
+            pre = head;
+            head = next;
+        }
+        return pre;
+    }
+
     /**
      * 功能描述 : 随机生成单链表
      * @author Leo
@@ -406,14 +438,14 @@ public class LinkedList {
         for (int i = 0; i < testTime; i++) {
             Node head = randomNode(maxSize, range);
             List<Node> nodeList = nodeToList(head);
-            Node node = reverseNode10(head);
+            Node node = reverseNode11(head);
             if (!verifyReverseListAndNode(nodeList, node)) {
                 System.out.println("nodeFuck!!");
                 break;
             }
             DoubleNode doubleNodeHead = randomDoubleNode(maxSize, range);
             List<DoubleNode> doubleNodeList = DoubleNodeToList(doubleNodeHead);
-            DoubleNode doubleNode = reverseDoubleNode6(doubleNodeHead);
+            DoubleNode doubleNode = reverseDoubleNode7(doubleNodeHead);
             if (!verifyReverseListAndDoubleNode(doubleNodeList, doubleNode)) {
                 System.out.println("doubleNodeFuck!!");
                 break;
diff --git a/src/leo/class06_09/IsPalindromeList.java b/src/leo/class06_09/IsPalindromeList.java
new file mode 100644
index 0000000..5a7b511
--- /dev/null
+++ b/src/leo/class06_09/IsPalindromeList.java
@@ -0,0 +1,423 @@
+package leo.class06_09;
+
+import com.sun.org.apache.xpath.internal.functions.FuncFalse;
+
+import javax.print.attribute.standard.NumberUp;
+import java.util.Stack;
+
+/**
+ * @author Leo
+ * @ClassName IsPalindromeList
+ * @DATE 2020/12/2 8:54 下午
+ * @Description
+ */
+public class IsPalindromeList {
+
+    public static boolean isPalindromeList(Node head) {
+        if (head == null || head.next == null) {
+            return true;
+        }
+        boolean verify = true;
+        Node mid = findMid(head);
+        Node midNext = mid.next;
+        mid.next = null;
+        midNext = reverseNode(midNext);
+        Node cur = head;
+        Node curReverseNode = midNext;
+        while (cur != null && curReverseNode != null) {
+            if (cur.value != curReverseNode.value) {
+                verify = false;
+                break;
+            }
+            cur = cur.next;
+            curReverseNode = curReverseNode.next;
+        }
+        midNext = reverseNode(midNext);
+        mid.next = midNext;
+        return verify;
+
+    }
+
+    public static Node findMid(Node head) {
+        if (head == null || head.next == null || head.next.next == null) {
+            return head;
+        }
+        Node slow = head;
+        Node fast = head;
+        while (fast.next != null && fast.next.next != null) {
+            slow = slow.next;
+            fast = fast.next.next;
+        }
+        return slow;
+    }
+
+    public static Node reverseNode(Node head) {
+        Node pre = null;
+        Node next = null;
+        while (head != null) {
+            next = head.next;
+            head.next = pre;
+            pre = head;
+            head = next;
+        }
+        return pre;
+    }
+
+    public static boolean isPalindromeListByStack(Node head) {
+        boolean verify = true;
+        Stack<Node> stack = new Stack<>();
+        Node cur = head;
+        while (cur != null) {
+            stack.push(cur);
+            cur = cur.next;
+        }
+        cur = head;
+        while (!stack.isEmpty()) {
+            if (stack.pop().value != cur.value) {
+                verify = false;
+            }
+            cur = cur.next;
+        }
+        return verify;
+    }
+
+
+    public static boolean isPalindromeList1(Node head){
+        if (head == null || head.next == null) {
+            return false;
+        }
+        Node n1 = head;
+        Node n2 = head;
+        while (n2.next != null && n2.next.next != null) {
+            n1 = n1.next;
+            n2 = n2.next.next;
+        }
+        n2 = n1.next;
+        n1.next = null;
+        Node n3 = null;
+        while (n2 != null) {
+            n3  = n2.next;
+            n2.next = n1;
+            n1 = n2;
+            n2 = n3;
+        }
+        n3 = n1;
+        n2 = head;
+        boolean verify = true;
+        while (n2 != null && n1 != null) {
+            if (n2.value != n1.value) {
+                verify = false;
+                break;
+            }
+            n1 = n1.next;
+            n2 = n2.next;
+        }
+
+
+        n1 = n3.next;
+        n3.next = null;
+        while (n1 != null) {
+            n2 = n1.next;
+            n1.next = n3;
+            n3 = n1;
+            n1 = n2;
+        }
+        return verify;
+    }
+
+
+    public static boolean isPalindromeList2(Node head){
+        if (head == null || head.next == null) {
+            return true;
+        }
+        Node n1 = head;
+        Node n2 = head;
+        //findMid
+        while (n2.next != null && n2.next.next != null) {
+            n1 = n1.next;
+            n2 = n2.next.next;
+        }
+        //n1 mid
+        //reverseNode half node
+        n2 = n1.next;   //n2 is after half head
+        //cut n1 is prefix half endNode
+        //and n1 is after half tail
+        n1.next = null;
+        //temp is next
+        Node n3 = null;
+        while (n2 != null) {
+            n3 = n2.next;
+            n2.next = n1;
+            n1 = n2;
+            n2 = n3;
+        }
+        //n2 is head of the flipped node
+        //n1 is the last node in the after half
+        n3 = n1; //save n1
+        n2 = head;
+        boolean verify = true;
+        while (n1 != null && n2 != null) {
+            if (n1.value != n2.value) {
+
+                verify = false;
+                break;
+            }
+            n1 = n1.next;
+            n2 = n2.next;
+        }
+        //reverseNode again
+        n1 = n3.next;
+        n3.next = null;
+        while (n1 != null) {
+            n2 = n1.next;
+            n1.next = n3;
+            n3 = n1;
+            n1 = n2;
+        }
+
+        return verify;
+
+    }
+
+
+    public static boolean isPalindromeList3(Node head) {
+        if (head == null || head.next == null) {
+            return true;
+        }
+        Node n1 = head;
+        Node n2 = head;
+        while (n2.next != null && n2.next.next != null) {
+            n1 = n1.next;
+            n2 = n2.next;
+        }
+        //n1 is mid;
+        n2 = n1.next;
+        n1.next = null;
+        Node n3 = null;
+        while (n2 != null) {
+            n3 = n2.next;
+            n2.next = n1;
+            n1 = n2;
+            n2 = n3;
+        }
+        n3 = n1;
+        n2 = head;
+        boolean verify = true;
+        while (n1 != null && n2 != null) {
+            if (n1.value != n2.value) {
+                verify = false;
+                break;
+            }
+            n1 = n1.next;
+            n2 = n2.next;
+        }
+        n1 = n3.next;
+        n3.next = null;
+        while (n1 != null) {
+            n2 = n1.next;
+            n1.next = n3;
+            n3 = n1;
+            n1 = n2;
+        }
+        return verify;
+
+    }
+
+    public static boolean isPalindromeList4(Node head) {
+        if (head == null || head.next == null) {
+            return true;
+        }
+        Node n1 = head;
+        Node n2 = head;
+        while (n2.next != null && n2.next.next != null) {
+            n1 = n1.next;
+            n2 = n2.next.next;
+        }
+        //reverseNode
+        //n1 is mid
+        n2 = n1.next;
+        n1.next = null;
+        Node n3 = null;
+        while (n2 != null) {
+            n3 = n2.next;
+            n2.next = n1;
+            n1 = n2;
+            n2 = n3;
+        }
+        n3 = n1;   //n1 is right
+        n2  = head; //left
+        boolean verify = true;
+        while (n1 != null && n2 != null) {
+            if (n1.value != n2.value) {
+                verify = false;
+                break;
+            }
+            n1 = n1.next;
+            n2 = n2.next;
+        }
+        n1 = n3.next;
+        n3.next = null;
+        while (n1 != null) {
+            n2 = n1.next;
+            n1.next = n3;
+            n3 = n1;
+            n1 = n2;
+        }
+        return verify;
+    }
+
+    public static boolean isPalindromeList5(Node head)  {
+        if (head == null || head.next == null) {
+            return true;
+        }
+        Node n1 = head;
+        Node n2 = head;
+        while (n2.next != null && n2.next.next != null) {
+            n1 = n1.next;
+            n2 = n2.next.next;
+        }
+        //n1 is mid
+        n2 = n1.next;
+        n1.next = null;
+        Node n3 = null;
+        while (n2 != null) {
+            n3 = n2.next;
+            n2.next = n1;
+            n1 = n2;
+            n2 = n3;
+        }
+        //n1 is head after flipping the linked list ;
+        //n1 and n2 end node is the same one
+        //n3 temporary save n1;
+        n3 = n1;
+        n2 = head;
+        boolean verify = true;
+        while (n1 != null && n2 != null) {
+            if (n1.value != n2.value) {
+                verify = false;
+            }
+            n1 = n1.next;
+            n2 = n2.next;
+        }
+        //if ListNode length is Even n2 is null ,
+        //if ListNode length is odd n1 and n2 both null
+        n2 = n3.next;
+        n3.next = null;
+        //reverse again
+        while (n2 != null) {
+            n1 = n2.next;
+            n2.next = n3;
+            n3 = n2;
+            n2 = n1;
+        }
+        return verify;
+    }
+
+}
+
+
+class IsPalindromeListMain {
+
+    public static void main(String[] args){
+        int testTime = 1000;
+        int maxSize = 3;
+        int range = 100;
+        boolean a;
+        boolean b;
+        System.out.println("start!");
+
+        for (int i = 0; i < testTime; i++) {
+            Node originNode = generateRandomNode(maxSize, range);
+            Node head = copyNode(originNode);
+            b = IsPalindromeList.isPalindromeListByStack(head);
+            a = IsPalindromeList.isPalindromeList5(head);
+            if (!isEqualsNode(head, originNode)) {
+                System.out.println("not equals node!");
+            }
+            if (a != b) {
+                System.out.println(a);
+                System.out.println(b);
+                System.out.println("fuck!");
+            }
+        }
+        System.out.println("end!");
+
+    }
+
+    private static boolean isEqualsNode(Node n1, Node n2) {
+        if (n1 == null && n2 == null) {
+            return true;
+        }
+        if (n1 != null && n2 == null) {
+            return false;
+        }
+
+        if (n1 == null && n2 != null) {
+            return false;
+        }
+        while (n1 != null && n2 != null) {
+            if (n1.value != n2.value) {
+                return false;
+            }
+            n1 = n1.next;
+            n2 = n2.next;
+        }
+
+        return true;
+    }
+
+    public static  Node generateRandomNode(int maxSize, int range) {
+        Node head = new Node(randomInt(range));
+        Node cur = head;
+        for (int i = 0; i < maxSize; i++) {
+            Node node = new Node(randomInt(range));
+            cur.next = node;
+            cur = cur.next;
+        }
+        if (Math.random() > 0.5) {
+            return head;
+        }
+        Node copyNode = copyNode(head);
+        copyNode = reverseNode(copyNode);
+        if (copyNode.next != null && Math.random() > 0.5) {
+            cur.next = copyNode.next;
+        }else{
+            cur.next = copyNode;
+        }
+        return head;
+    }
+
+    private static Node copyNode(Node head) {
+        Node copyHead = new Node(head.value);
+        Node curCopy = copyHead;
+        Node curHead = head.next;
+        while (curHead.next != null) {
+            curCopy.next = new Node(curHead.value);
+            curHead = curHead.next;
+            curCopy = curCopy.next;
+        }
+        curCopy.next = new Node(curHead.value);
+        return copyHead;
+    }
+
+
+    private static Node reverseNode(Node head) {
+        if (head == null || head.next == null) {
+            return head;
+        }
+        Node pre = null;
+        Node next = null;
+        while (head != null) {
+            next = head.next;
+            head.next = pre;
+            pre = head;
+            head = next;
+        }
+        return pre;
+    }
+
+    public static int randomInt(int range) {
+        return (int) ((range * Math.random() + 1) - (range * Math.random() + 1));
+    }
+
+}
diff --git a/src/leo/class06_09/LinkedListMid.java b/src/leo/class06_09/LinkedListMid.java
new file mode 100644
index 0000000..8d461fb
--- /dev/null
+++ b/src/leo/class06_09/LinkedListMid.java
@@ -0,0 +1,210 @@
+package leo.class06_09;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * @author Leo
+ * @ClassName class06_09
+ * @DATE 2020/12/2 6:42 下午
+ * @Description 找链表中点
+ */
+class LinkedListMid {
+
+
+    //奇数长度返回中点，偶数长度返回上中点
+    static class FindMidOrUpMidNode{
+        public static Node findMid(Node head){
+            if (head == null || head.next == null || head.next.next == null) {
+                return head;
+            }
+            Node slow = head;
+            Node fast = head;
+            while (fast.next != null && fast.next.next != null) {
+                slow = slow.next;
+                fast = fast.next.next;
+            }
+            return slow;
+        }
+    }
+
+    //奇数长度返回中点，偶数长度返回下中点
+    static class FindMidOrDownMidNode{
+        public static Node findMid(Node head) {
+            if (head == null || head.next == null) {
+
+                return head;
+            }
+            Node slow = head.next;
+            Node fast = head.next;
+            while (fast.next != null && fast.next.next != null) {
+                slow = slow.next;
+                fast = fast.next.next;
+            }
+            return slow;
+        }
+
+    }
+
+    //奇数长度返回中点前一个，偶数长度返回上中点前一个
+    static class FindMidOrUpMidPreNode {
+        public static Node findMid(Node head) {
+            if (head==null||head.next==null||head.next.next==null){
+                return head;
+            }
+            Node slow = head;
+            Node fast = head.next.next;
+            while (fast.next != null && fast.next.next != null) {
+                slow = slow.next;
+                fast = fast.next.next;
+            }
+            return slow;
+        }
+    }
+
+    //奇数长度返回中点前一个，偶数长度返回下中点前一个
+    static class FindMidOrDownMidPreNode {
+        public static Node findMid(Node head) {
+            if (head == null || head.next == null || head.next.next == null) {
+                return head;
+            }
+            Node slow = head;
+            Node fast = head.next;
+            while (fast.next != null && fast.next.next != null) {
+                slow = slow.next;
+                fast = fast.next.next;
+            }
+            return slow;
+        }
+
+    }
+
+
+}
+
+class Right{
+    //奇数长度返回中点，偶数长度返回上中点
+    public static Node findMidOrUpMidNode(Node head) {
+        if (head == null) {
+            return head;
+        }
+        List<Node> list = new ArrayList<>();
+        Node cur = head;
+        while (cur != null) {
+            list.add(cur);
+            cur = cur.next;
+        }
+        return list.get((list.size()-1) /2);
+    }
+
+    //奇数长度返回中点，偶数长度返回下中点
+    public static Node findMidOrDownMidNode(Node head) {
+        if (head == null) {
+            return head;
+        }
+        List<Node> list = new ArrayList<>();
+        Node cur = head;
+        while (cur != null) {
+            list.add(cur);
+            cur = cur.next;
+        }
+        return list.get(list.size()/2);
+    }
+    //奇数长度返回中点前一个，偶数长度返回上中点前一个
+    public static Node findMidOrUpMidPreNode(Node head){
+        if (head == null) {
+            return head;
+        }
+        List<Node> list = new ArrayList<>();
+        Node cur = head;
+        while (cur != null) {
+            list.add(cur);
+            cur = cur.next;
+        }
+        return list.get((list.size()-3)/2);
+
+    }
+    //奇数长度返回中点前一个，偶数长度返回下中点前一个
+    public static Node findMidOrDownMidPreNode(Node head){
+        if (head == null) {
+            return head;
+        }
+        List<Node> list = new ArrayList<>();
+        Node cur = head;
+        while (cur != null) {
+            list.add(cur);
+            cur = cur.next;
+        }
+        return list.get((list.size()-2)/2);
+
+    }
+}
+
+class LinkedListMidMain{
+
+
+    public static Node randomNode(int maxSize, int range) {
+        int length = (int)(maxSize * Math.random()) + 1;
+        Node head = new Node((int) (range * Math.random()) + 1 - (int) (range * Math.random()) + 1);
+        Node cur = head;
+        for (int i = 0; i < length; i++) {
+            Node node = new Node((int) (range * Math.random()) + 1 - (int) (range * Math.random()) + 1);
+            cur.next = node;
+            cur = cur.next;
+        }
+        return head;
+    }
+
+    public static void main(String[] args){
+        int testTime = 100000;
+        int maxSize = 80;
+        int range = 100;
+        Node node;
+        Node nodeTest;
+        System.out.println("start!");
+
+        for (int i = 0; i < testTime; i++) {
+            Node head = randomNode(maxSize, range);
+            node = LinkedListMid.FindMidOrUpMidNode.findMid(head);
+            nodeTest = Right.findMidOrUpMidNode(head);
+            if (!node.equals(nodeTest)){
+                System.out.println("findMidOrUpMidNode");
+                System.out.println(node.toString());
+                System.out.println(nodeTest.toString());
+                break;
+            }
+            node = LinkedListMid.FindMidOrDownMidNode.findMid(head);
+            nodeTest = Right.findMidOrDownMidNode(head);
+            if (!node.equals(nodeTest)){
+                System.out.println("findMidOrDownMidNode");
+                System.out.println(node.toString());
+                System.out.println(nodeTest.toString());
+                break;
+            }
+            node = LinkedListMid.FindMidOrUpMidPreNode.findMid(head);
+            nodeTest = Right.findMidOrUpMidPreNode(head);
+            if (!node.equals(nodeTest)){
+                System.out.println("findMidOrUpMidPreNode");
+                System.out.println(node.toString());
+                System.out.println(nodeTest.toString());
+                break;
+            }
+            node = LinkedListMid.FindMidOrDownMidPreNode.findMid(head);
+            nodeTest = Right.findMidOrDownMidPreNode(head);
+            if (!node.equals(nodeTest)){
+                System.out.println("findMidOrDownMidPreNode");
+                System.out.println(node.toString());
+                System.out.println(nodeTest.toString());
+                break;
+            }
+        }
+        System.out.println("end!");
+
+    }
+
+
+
+
+
+
+}
diff --git a/src/leo/class06_09/Node.java b/src/leo/class06_09/Node.java
new file mode 100644
index 0000000..a325757
--- /dev/null
+++ b/src/leo/class06_09/Node.java
@@ -0,0 +1,40 @@
+package leo.class06_09;
+
+/**
+ * @author Leo
+ * @ClassName Node
+ * @DATE 2020/12/2 8:56 下午
+ * @Description
+ */
+public class Node{
+    int value;
+    Node next;
+    public Node(int v){
+        this.value = v;
+    }
+
+    @Override
+    public boolean equals(Object object) {
+        if (this == object) return true;
+        if (object == null || getClass() != object.getClass()) return false;
+
+        Node node = (Node) object;
+
+        if (value != node.value) return false;
+        return next.equals(node.next);
+    }
+
+    @Override
+    public int hashCode() {
+        int result = value;
+        result = 31 * result + next.hashCode();
+        return result;
+    }
+
+    @Override
+    public String toString() {
+        return "Node{" +
+                "value=" + value +
+                '}';
+    }
+}
diff --git a/src/leo/class06_09/SmallerEqualBigger.java b/src/leo/class06_09/SmallerEqualBigger.java
new file mode 100644
index 0000000..c3a2054
--- /dev/null
+++ b/src/leo/class06_09/SmallerEqualBigger.java
@@ -0,0 +1,195 @@
+package leo.class06_09;
+
+/**
+ * @author Leo
+ * @ClassName SmallerEqualBigger
+ * @DATE 2020/12/3 5:56 下午
+ * @Description 将链表根据给定值,按小左大右放置
+ */
+public class SmallerEqualBigger {
+
+
+
+    static class NodePartitionByArray{
+
+        public static Node nodePartitionByArray(Node head, int target) {
+            if (head == null || head.next == null) {
+                return head;
+            }
+            int i = 0;
+            Node cur = head;
+            while (cur != null) {
+                cur = cur.next;
+                i++;
+            }
+            Node[] nodes = new Node[i];
+            cur = head;
+            for (i = 0; i < nodes.length; i++) {
+                nodes[i] = cur;
+                cur = cur.next;
+            }
+            partitionNode(nodes, target);
+            for (i = 1; i < nodes.length; i++) {
+                nodes[i - 1].next = nodes[i];
+            }
+            nodes[i - 1].next = null;
+            return nodes[0];
+        }
+
+        public static void partitionNode(Node[] nodes, int target) {
+            int small = -1;
+            int big = nodes.length;
+            int index = 0;
+            while (index < big) {
+                if (nodes[index].value < target) {
+                    swapNodeArray(nodes, index++, ++small);
+                } else if (nodes[index].value > target) {
+                    swapNodeArray(nodes, index, --big);
+                }else {
+                    index++;
+                }
+            }
+        }
+
+        public static void swapNodeArray(Node[] nodes, int i, int j) {
+
+            if (i == j) {
+                return;
+            }
+            Node temp = nodes[i];
+            nodes[i] = nodes[j];
+            nodes[j] = temp;
+        }
+    }
+
+    public static Node listPartition(Node head, int target) {
+        if (head == null || head.next == null) {
+            return head;
+        }
+        Node sH = null;
+        Node sT = null;
+        Node bH = null;
+        Node bT = null;
+        Node next = null;
+        while (head != null) {
+            next = head.next;
+            head.next = null;
+            if (head.value < target) {
+                if (sH == null) {
+                    sH = head;
+                    sT = head;
+                }else{
+                    sT.next = head;
+                    sT = head;
+                }
+            } else if (head.value > target) {
+                if (bH == null) {
+                    bH = head;
+                    bT = head;
+                }else {
+                    bT.next = head;
+                    bT = head;
+                }
+
+            } else if (head.value == target) {
+                if (bH == null) {
+                    bH = head;
+                    bT = head;
+                }else{
+                    head.next = bH;
+                    bH = head;
+                }
+            }
+            head = next;
+        }
+        if (sT == null) {
+            return bH;
+        } else {
+            sT.next = bH;
+            return sH;
+        }
+    }
+}
+
+class SmallerEqualBigger_Main{
+    public static void printLinkedList(Node node) {
+        System.out.print("Linked List: ");
+        while (node != null) {
+            System.out.print(node.value + " ");
+            node = node.next;
+        }
+        System.out.println();
+    }
+
+    public static void main(String[] args) {
+
+        int maxSize = 5;
+        int range = 100;
+        Node originNode = generateRandomNode(maxSize, range);
+        printLinkedList(originNode);
+        // head1 = listPartition1(head1, 4);
+        int i = randomInt(range);
+        System.out.println(i);
+        originNode = SmallerEqualBigger.listPartition(originNode, i);
+        printLinkedList(originNode);
+
+    }
+
+    public static  Node generateRandomNode(int maxSize, int range) {
+        Node head = new Node(randomInt(range));
+        Node cur = head;
+        for (int i = 0; i < maxSize; i++) {
+            Node node = new Node(randomInt(range));
+            cur.next = node;
+            cur = cur.next;
+        }
+        if (Math.random() > 0.5) {
+            return head;
+        }
+        Node copyNode = copyNode(head);
+        copyNode = reverseNode(copyNode);
+        if (copyNode.next != null && Math.random() > 0.5) {
+            cur.next = copyNode.next;
+        }else{
+            cur.next = copyNode;
+        }
+        return head;
+    }
+
+    private static Node copyNode(Node head) {
+        Node copyHead = new Node(head.value);
+        Node curCopy = copyHead;
+        Node curHead = head.next;
+        while (curHead.next != null) {
+            curCopy.next = new Node(curHead.value);
+            curHead = curHead.next;
+            curCopy = curCopy.next;
+        }
+        curCopy.next = new Node(curHead.value);
+        return copyHead;
+    }
+
+
+    private static Node reverseNode(Node head) {
+        if (head == null || head.next == null) {
+            return head;
+        }
+        Node pre = null;
+        Node next = null;
+        while (head != null) {
+            next = head.next;
+            head.next = pre;
+            pre = head;
+            head = next;
+        }
+        return pre;
+    }
+
+    public static int randomInt(int range) {
+        return (int) ((range * Math.random() + 1) - (range * Math.random() + 1));
+    }
+
+}
+
+
+