20240712 Finished

LeetCodeSharp/Problems/Solution23.cs

@@ -0,0 +1,77 @@
+// [23] Merge k Sorted Lists
+
+using LeetCodeSharp.Utils;
+
+namespace LeetCodeSharp.Problems23
+{
+    // Submission codes start here
+
+    /**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     public int val;
+ *     public ListNode next;
+ *     public ListNode(int val=0, ListNode next=null) {
+ *         this.val = val;
+ *         this.next = next;
+ *     }
+ * }
+ */
+    public class Solution
+    {
+        private ListNode MergeTwoLists(ListNode a, ListNode b)
+        {
+            if (a == null || b == null)
+            {
+                return a ?? b;
+            }
+
+            var dummyHead = new ListNode();
+            var node = dummyHead;
+
+            while (a != null && b != null)
+            {
+                if (a.val < b.val)
+                {
+                    node.next = a;
+                    a = a.next;
+                }
+                else
+                {
+                    node.next = b;
+                    b = b.next;
+                }
+
+                node = node.next;
+            }
+
+            node.next = a ?? b;
+
+            return dummyHead.next;
+        }
+
+        private ListNode Merge(ListNode[] lists, int l, int r)
+        {
+            if (l == r)
+            {
+                return lists[l];
+            }
+
+            if (l > r)
+            {
+                return null;
+            }
+
+            var middle = (l + r) / 2;
+
+            return MergeTwoLists(Merge(lists, l, middle), Merge(lists, middle + 1, r));
+        }
+
+        public ListNode MergeKLists(ListNode[] lists)
+        {
+            return Merge(lists, 0, lists.Length - 1);
+        }
+    }
+
+    // Submission codes end here
+}