Add ListNode and LinkedListTest

src/main/java/org/example/ListNode.java

@@ -0,0 +1,28 @@
+package org.example;
+
+public class ListNode {
+
+    public int value;
+    public ListNode next;
+
+    public ListNode() {
+    }
+
+    public ListNode(int value) {
+        this.value = value;
+    }
+
+    public ListNode(int value, ListNode next) {
+        this.value = value;
+        this.next = next;
+    }
+
+    @Override
+    public String toString() {
+        return "ListNode[" + value + "]";
+    }
+
+    public String toDetailString() {
+        return "ListNode[v=" + value + ", next=" + next + "]";
+    }
+}

src/test/java/LinkedListTest.java

@@ -0,0 +1,63 @@
+import static support.ListNodeSupport.NODE_1;
+import static support.ListNodeSupport.NODE_2;
+import static support.ListNodeSupport.NODE_3;
+import static support.ListNodeSupport.NODE_4;
+
+import java.util.ArrayList;
+import java.util.List;
+import org.example.ListNode;
+import org.junit.jupiter.api.Test;
+import support.ListNodeSupport;
+
+public class LinkedListTest {
+
+    /**
+     * https://leetcode.com/problems/reorder-list/
+     */
+    @Test
+    void reorderList() {
+        ListNode head = ListNodeSupport.linkNext(NODE_1, NODE_2, NODE_3, NODE_4);
+        System.out.println("head = " + head.toDetailString());
+
+//        0,1,2,3
+//        0,3   - left=0, right=3
+//        0,3,1 - left=1, right=3
+//        0,3,1,2 - left=1, right=2
+//        0,3,1,2 [end] - left=2, right=2
+
+//        0,1,2,3,4
+//        0,5 - left=0, right=4
+//        0,5,1 - left=1, right=4
+//        0,5,1,4 - left=1, right=3
+//        0,5,1,4,2 - left=2, right=3
+//        0,5,1,4,2,3 - left=2, right=2
+//        0,5,1,4,2,3 [end] - left=3, right=3
+
+        if (head.next == null) {
+            return;
+        }
+        List<ListNode> nodes = new ArrayList<>();
+        ListNode reorderHead = head;
+        ListNode reorderHead2 = head;
+        while (head != null) {
+            ListNode next = head.next;
+            head.next = null;
+            nodes.add(head);
+            head = next;
+        }
+
+        int left = 0;
+        int right = nodes.size() - 1;
+        while (left < right) {
+            reorderHead.next = nodes.get(right);
+            right--;
+            left++;
+            if (left <= right && left < nodes.size()) {
+                reorderHead = reorderHead.next;
+                reorderHead.next = nodes.get(left);
+                reorderHead = reorderHead.next;
+            }
+        }
+        System.out.println("reorderHead = " + reorderHead2);
+    }
+}

src/test/java/support/ListNodeSupport.java

@@ -0,0 +1,33 @@
+package support;
+
+import java.util.Arrays;
+import java.util.List;
+import org.example.ListNode;
+
+public class ListNodeSupport {
+
+    public static final ListNode NODE_1 = new ListNode(1);
+    public static final ListNode NODE_2 = new ListNode(2);
+    public static final ListNode NODE_3 = new ListNode(3);
+    public static final ListNode NODE_4 = new ListNode(4);
+    public static final ListNode NODE_5 = new ListNode(5);
+    public static final ListNode NODE_6 = new ListNode(6);
+    public static final ListNode NODE_7 = new ListNode(7);
+    public static final ListNode NODE_8 = new ListNode(8);
+    public static final ListNode NODE_9 = new ListNode(9);
+    public static final ListNode NODE_10 = new ListNode(10);
+
+    public static ListNode from(int val) {
+        return new ListNode(val);
+    }
+
+    public static ListNode linkNext(ListNode... nodes) {
+        List<ListNode> list = Arrays.stream(nodes)
+                                    .toList();
+
+        for (int i = 0; i < list.size() - 1; i++) {
+            list.get(i).next = list.get(i + 1);
+        }
+        return list.get(0);
+    }
+}