Day i do not know

299. Bulls and Cows/299. Bulls and Cows.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <RootNamespace>_299._Bulls_and_Cows</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

299. Bulls and Cows/Program.cs

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+namespace _299._Bulls_and_Cows;
+
+internal class Program
+{
+    static void Main(string[] args)
+    {
+        Console.WriteLine(new Solution().GetHint("1123", "0111"));
+    }
+}

299. Bulls and Cows/Solution.cs

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+using System.Text;
+
+namespace _299._Bulls_and_Cows;
+
+public class Solution
+{
+    public string GetHint(string secret, string guess)
+    {
+        StringBuilder secretSb = new StringBuilder(secret);
+        StringBuilder guessSb = new StringBuilder(guess);
+
+        Dictionary<char, int> secretCount = new Dictionary<char, int>();
+        Dictionary<char, int> guessCount = new Dictionary<char, int>();
+        int A = 0;
+        int B = 0;
+        for(int i = 0; i < secret.Length + 1; i++)
+        {
+            if (i < secret.Length && secretSb[i] == guessSb[i])
+            {
+                secretSb[i] = '*';
+                guessSb[i] = '*';
+                A++;
+            }
+            if (i > 0)
+            {
+                int index = i - 1;
+                if (secretSb[index] == '*')
+                    continue;
+                char key1 = secretSb[index];
+                if (secretCount.ContainsKey(key1))
+                    secretCount[key1]++;
+                else
+                    secretCount.Add(key1, 1);
+
+                char key2 = guessSb[index];
+                if (guessCount.ContainsKey(key2))
+                    guessCount[key2]++;
+                else
+                    guessCount.Add(key2, 1);
+            }
+        }
+        foreach (var kp in secretCount)
+        {
+            if (guessCount.ContainsKey(kp.Key) == false)
+                continue;
+            B += Math.Min(kp.Value, guessCount[kp.Key]);
+        }
+        return $"{A}A{B}B";
+    }
+}