Initial commit

217. Contains Duplicate/217. Contains Duplicate.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <RootNamespace>_217._Contains_Duplicate</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

217. Contains Duplicate/Program.cs

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+namespace _217._Contains_Duplicate
+{
+    internal class Program
+    {
+        static void Main(string[] args)
+        {
+            Console.WriteLine("Hello, World!");
+        }
+    }
+}

217. Contains Duplicate/Solution.cs

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+namespace _217._Contains_Duplicate;
+
+public class Solution
+{
+    public bool ContainsDuplicate(int[] nums)
+    {
+        return nums.ToHashSet().Count != nums.Length;
+    }
+}