Day i do not know

136. Single Number/136. Single Number.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <RootNamespace>_136._Single_Number</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

136. Single Number/Program.cs

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+namespace _136._Single_Number;
+
+internal class Program
+{
+    static void Main(string[] args)
+    {
+        Console.WriteLine("Hello, World!");
+    }
+}

136. Single Number/Solution.cs

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+namespace _136._Single_Number;
+
+public class Solution
+{
+    public int SingleNumber(int[] nums)
+    {
+        int res = 0;
+        foreach (int num in nums)
+            res ^= num;
+        return res;
+    }
+}