Day3. Start Algorithm

278. First Bad Version/278. First Bad Version.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <RootNamespace>_278._First_Bad_Version</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

278. First Bad Version/Program.cs

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+namespace _278._First_Bad_Version
+{
+    internal class Program
+    {
+        static void Main(string[] args)
+        {
+            Console.WriteLine(new Solution().FirstBadVersion(2147483647, 2147483647));
+        }
+    }
+}

278. First Bad Version/Solution.cs

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+namespace _278._First_Bad_Version;
+
+public class VersionControl
+{
+    protected int _badVersion = 0;
+    protected bool IsBadVersion(int version) => version >= _badVersion;
+}
+
+public class Solution : VersionControl
+{
+    public int FirstBadVersion(int n)
+    {
+        long l = -1;
+        long r = n;
+        while (l != r - 1)
+        {
+            long i = (r + l) / 2;
+            bool res = IsBadVersion((int)i);
+            if (res)
+                r = i;
+            else
+                l = i;
+        }
+        return (int)l + 1;
+    }
+
+    public int FirstBadVersion(int n, int bad)
+    {
+        _badVersion = bad;
+        return FirstBadVersion(n);
+    }
+}
+