doc: 2025-10-24打卡

143.reorder-list.java

@@ -0,0 +1,52 @@
+/*
+ * @lc app=leetcode id=143 lang=java
+ *
+ * [143] Reorder List
+ */
+
+// @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 void reorderList(ListNode head) {
+        if(head == null || head.next == null) {
+            return;
+        }
+        // reverse the right side and merge
+        ListNode d1 = new ListNode(0);
+        d1.next = head;
+        ListNode slow = d1, fast = d1;
+        while(fast!=null && fast.next!=null) {
+            fast = fast.next.next;
+            slow = slow.next;
+        }
+        ListNode rh = slow.next, lh = head;
+        slow.next = null;
+        // reverse the right half
+        ListNode prev = null, cur = rh, t;
+        while(cur != null) {
+            t = cur.next;
+            cur.next = prev;
+            prev = cur;
+            cur = t;
+        }
+        rh = prev;
+        // merge the two linkedlist
+        while(rh != null) {
+            t = lh.next;
+            lh.next = rh;
+            lh = rh;
+            rh = t;
+        }
+    }
+}
+// @lc code=end
+