Create 23-Merge-k-Sorted-Lists.cs

Author: qwmhq

csharp/23-Merge-k-Sorted-Lists.cs

@@ -0,0 +1,65 @@
+/**
+ * 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 {
+    public ListNode MergeKLists(ListNode[] lists) {
+        if (lists.Length == 0)
+        {
+            return null;
+        }
+        
+        while (lists.Length > 1)
+        {
+            var mergedLists = new ListNode[(lists.Length + 1) / 2];
+            for (int i = 0; i < lists.Length; i += 2)
+            {
+                var l1 = lists[i];
+                var l2 = (i + 1 < lists.Length) ? lists[i + 1] : null;
+                mergedLists[i/2] = (MergeLists(l1, l2));
+            }
+            lists = mergedLists;
+        }
+        
+        return lists[0];
+    }
+    
+    public ListNode MergeLists(ListNode l1, ListNode l2)
+    {
+        var sorted = new ListNode();
+        var current = sorted;
+        
+        while (l1 != null && l2 != null)
+        {
+            if (l1.val <= l2.val)
+            {
+                current.next = l1;
+                l1 = l1.next;
+            }
+            else
+            {
+                current.next = l2;
+                l2 = l2.next;
+            }
+            current = current.next;
+        }
+        
+        if (l1 != null)
+        {
+            current.next = l1;
+        } else 
+        {
+            current.next = l2;
+        }
+        
+        return sorted.next;
+    }
+}