doc: 2025-10-24打卡

24.swap-nodes-in-pairs.java

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+/*
+ * @lc app=leetcode id=24 lang=java
+ *
+ * [24] Swap Nodes in Pairs
+ */
+
+// @lc code=start
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Solution {
+    public ListNode swapPairs(ListNode head) {
+        ListNode dummy = new ListNode(0);
+        dummy.next = head;
+        ListNode prev = dummy, cur = head, next = head == null ? null : head.next, t;
+        while(cur !=null && next != null) {
+            prev.next = next;
+            t = next.next;
+            next.next = cur;
+            cur.next = t;
+
+            prev = cur;
+            cur = cur.next;
+            next = cur == null ? null : cur.next;
+        }
+        return dummy.next;
+    }
+}
+// @lc code=end
+