feat: 2025-10-29打卡

23.merge-k-sorted-lists.java

@@ -0,0 +1,66 @@
+/*
+ * @lc app=leetcode id=23 lang=java
+ *
+ * [23] Merge k Sorted Lists
+ */
+
+// @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 mergeKLists(ListNode[] lists) {
+        if(lists == null || lists.length == 0) {
+            return null;
+        }
+        return mergeRecursively(lists, 0, lists.length-1);
+    }
+
+    private ListNode mergeRecursively(ListNode[] lists, int i, int j) {
+        if (i > j) {
+            return null;
+        }else if(i == j) {
+            return lists[i];
+        } else if (j - i == 1) {
+            return merge(lists[i], lists[j]);
+        }
+        int m = (i+j)/2;
+        return merge(mergeRecursively(lists, i, m), mergeRecursively(lists, m+1, j));
+    }
+
+    private ListNode merge(ListNode l1, ListNode l2) {
+        ListNode dummy = new ListNode(0), tail = dummy;
+        dummy.next = null;
+        while(l1 != null || l2 != null) {
+            if(l1 == null || l2 == null) {
+                if(l1 != null) {
+                    tail.next = l1;
+                } else if(l2 != null) {
+                    tail.next = l2;
+                }
+                break;
+            }
+            if(l1.val <= l2.val) {
+                tail.next = l1;
+                l1 = l1.next;
+                tail = tail.next;
+                tail.next = null;
+            } else {
+                tail.next = l2;
+                l2 = l2.next;
+                tail = tail.next;
+                tail.next = null;
+            }
+        }
+        return dummy.next;
+    }
+}
+// @lc code=end
+

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
+

92.reverse-linked-list-ii.java

@@ -26,15 +26,18 @@ class Solution {
     public ListNode reverseBetween(ListNode head, int left, int right) {
         ListNode dummy = new ListNode(0);
         dummy.next = head;
-        ListNode prev = dummy;
-        for(int i = 0; i< left-1; i++) {
+        ListNode prev, frm;
+        prev = frm = dummy;
+        for(int i = 0; i<left-1; i++) {
             prev = prev.next;
         }
-        ListNode cur = prev.next;
-        ListNode tail = cur, tmp;
-        for(int i = 0; i < right-left; i++) {
-            cur = tail.next;
-            tail.next = cur.next;
+        for(int i = 0; i < left; i++) {
+            frm = frm.next;
+        }
+        ListNode cur;
+        for(int i = 0; i<right-left; i++) {
+            cur = frm.next;
+            frm.next = cur.next;
             cur.next = prev.next;
             prev.next = cur;
         }