24.8.23 LeetCode Hot100 linkedList

src/main/java/com/cool/Template.java

@@ -1,13 +1,14 @@
 package com.cool;
-
+/**
+ * DayNumber 1/2/3/4
+ * @author Cool
+ * @date 2024/8/19
+ * hard  1/2/3
+ *
+ */
 public class Template {
 
-    /**
-     * Date 2924/8/19
-     * DayNumber 1/2/3/4
-     * hard  1
-     * @param template
-     */
+
     public void test(int template){
 
     }

src/main/java/com/cool/hot100/linkedlist/Num24.java

@@ -0,0 +1,54 @@
+package com.cool.hot100.linkedlist;
+
+import org.junit.Test;
+
+public class Num24 {
+    /**
+     * Date 2024/8/23
+     * DayNumber 1
+     * Hard 2
+     *
+     * @param head
+     * @return
+     */
+    public ListNode swapPairs(ListNode head) {
+        ListNode node = head;
+        ListNode newHead = null;
+        ListNode pre = null;
+        while (node != null) {
+            if (node.next != null) {
+                ListNode next = node.next;
+                node.next = next.next;
+                next.next = node;
+                if (pre == null) {
+                    pre = node;
+                } else {
+                    pre.next = next;
+                    pre = node;
+                }
+                node = node.next;
+                if (newHead == null) {
+                    newHead = next;
+                }
+
+
+            } else {
+                break;
+            }
+        }
+        return newHead == null ? head : newHead;
+    }
+
+    @Test
+    public void test() {
+        ListNode node1 = new ListNode(2);
+        ListNode node2 = new ListNode(2, node1);
+        ListNode node3 = new ListNode(6, node2);
+        ListNode node4 = new ListNode(4, node3);
+        ListNode node5 = new ListNode(3, node4);
+        ListNode node6 = new ListNode(5, node5);
+        ListNode node7 = new ListNode(2, node6);
+        swapPairs(node7);
+    }
+
+}