力扣：24. 两两交换链表中的节点

LeetCode/src/main/java/com/code/leet/study/t20210208/SwapPairs.java

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+package com.code.leet.study.t20210208;
+
+import com.code.leet.entiy.ListNode;
+
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * 给定一个链表，两两交换其中相邻的节点，并返回交换后的链表。
+ * <p>
+ * 你不能只是单纯的改变节点内部的值，而是需要实际的进行节点交换。
+ */
+public class SwapPairs {
+    /**
+     * 24. 两两交换链表中的节点
+     */
+//    public ListNode swapPairs(ListNode head) {
+//        if (head == null || head.next == null) {
+//            return head;
+//        }
+//        ListNode newHead = head.next;
+//        head.next = swapPairs(newHead.next);
+//        newHead.next = head;
+//        return newHead;
+//    }
+    public ListNode swapPairs(ListNode head) {
+        if (head == null || head.next == null) {
+            return head;
+        }
+        ListNode newHead = new ListNode(0);
+        ListNode temp = newHead;
+        while (head != null) {
+            if(head.next==null){
+                break;
+            }
+            ListNode after = head.next.next;
+            ListNode next = head.next;
+
+            head.next = after;
+            next.next = head;
+
+            temp.next = next;
+            temp = temp.next.next;
+            head = head.next;
+        }
+        return newHead.next;
+    }
+
+//    public static void main(String[] args) {
+//        List<Integer> list = Arrays.asList(1,2,3,4);
+//        ListNode head = new ListNode(list.get(0));
+//        ListNode newHead = head;
+//        for (int i = 1; i < list.size(); i++) {
+//            newHead.next = new ListNode(list.get(i));
+//            newHead = newHead.next;
+//        }
+//        swapPairs(head);
+//    }
+}