Day3. Start Algorithm

21. Merge Two Sorted Lists/21. Merge Two Sorted Lists.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <RootNamespace>_21._Merge_Two_Sorted_Lists</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

21. Merge Two Sorted Lists/ListNode.cs

@@ -0,0 +1,37 @@
+namespace _21._Merge_Two_Sorted_Lists;
+
+//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 static ListNode Create(int[] nums)
+    {
+        ListNode l = new ListNode(nums[0]);
+        ListNode cur = l;
+        for (int i = 1; i < nums.Length; i++)
+        {
+            cur.next = new ListNode(nums[i]);
+            cur = cur.next;
+        }
+        return l;
+    }
+
+    public override string ToString()
+    {
+        List<int> list = new List<int>();
+        ListNode? cur = this;
+        while (cur != null)
+        {
+            list.Add(cur.val);
+            cur = cur.next;
+        }
+        return String.Join(" ", list);
+    }
+}

21. Merge Two Sorted Lists/Program.cs

@@ -0,0 +1,12 @@
+namespace _21._Merge_Two_Sorted_Lists
+{
+    internal class Program
+    {
+        static void Main(string[] args)
+        {
+            var l1 = ListNode.Create(new int[] { 1, 2, 4 });
+            var l2 = ListNode.Create(new int[] { 1, 3, 4 });
+            Console.WriteLine(new Solution().MergeTwoLists(l1, l2));
+        }
+    }
+}

21. Merge Two Sorted Lists/Solution.cs

@@ -0,0 +1,44 @@
+namespace _21._Merge_Two_Sorted_Lists;
+
+public class Solution
+{
+    public ListNode MergeTwoLists(ListNode? list1, ListNode? list2)
+    {
+        ListNode? start = null;
+        ListNode? current = null;
+        List<ListNode?> listNodes = new List<ListNode?>() { list1, list2 };
+        while (listNodes.Any(l => l != null))
+        {
+            int i = MinIndex(listNodes);
+            ListNode? curMin = listNodes[i];
+            listNodes[i] = listNodes[i]!.next;
+
+            if (start == null)
+            {
+                start = curMin;
+                current = start;
+            }
+            else if (current != null)
+            {
+                current.next = curMin;
+                current = current.next;
+            }
+        }
+        return start!;
+    }
+
+    private int MinIndex(List<ListNode?> list)
+    {
+        int minValue = int.MaxValue;
+        int index = -1;
+        for (int i = 0; i < list.Count; i++)
+        {
+            if (list[i]?.val < minValue)
+            {
+                minValue = list[i]!.val;
+                index = i;
+            }
+        }
+        return index;
+    }
+}