feat: 2025-10-29打卡

25.reverse-nodes-in-k-group.java

@@ -0,0 +1,48 @@
+/*
+ * @lc app=leetcode id=25 lang=java
+ *
+ * [25] Reverse Nodes in k-Group
+ */
+
+// @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 reverseKGroup(ListNode head, int k) {
+        ListNode dummy = new ListNode(0), prev, frm, to;
+        dummy.next = head;
+        prev = dummy;
+        while(prev.next != null) {
+            frm = to = prev.next;
+            for(int i = 0; i<k-1; i++) {
+                if(to!=null) {
+                    to = to.next;
+                }
+            }
+            if(to == null) {
+                // reach the end
+                break;
+            }
+            // reverse nodes in [frm, to]
+            ListNode cur = frm.next;
+            for(int i = 0; i<k-1; i++) {
+                frm.next = cur.next;
+                cur.next = prev.next;
+                prev.next = cur;
+                cur = frm.next;
+            }
+            prev = frm;
+        }
+        return dummy.next;
+    }
+}
+// @lc code=end
+