Day i do not know

424. Longest Repeating Character Replacement/424. Longest Repeating Character Replacement.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <RootNamespace>_424._Longest_Repeating_Character_Replacement</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

424. Longest Repeating Character Replacement/Program.cs

@@ -0,0 +1,9 @@
+namespace _424._Longest_Repeating_Character_Replacement;
+
+internal class Program
+{
+    static void Main(string[] args)
+    {
+        Console.WriteLine(new Solution().CharacterReplacement("ABAB", 2));
+    }
+}

424. Longest Repeating Character Replacement/Solution.cs

@@ -0,0 +1,56 @@
+namespace _424._Longest_Repeating_Character_Replacement;
+
+public class Solution
+{
+    public int CharacterReplacement(string s, int k)
+    {
+        List<Counter> counters = new List<Counter>();
+        int max = 0;
+        for (int i = 0; i < s.Length; i++)
+        {
+            char ch = s[i];
+            for (int cIndex = 0; cIndex < counters.Count; cIndex++)
+            {
+                Counter curC = counters[cIndex];
+                curC.Add(ch);
+                if (curC.IsValid == false)
+                {
+                    max = Math.Max(max, curC.ValidLength);
+                    counters.RemoveAt(cIndex);
+                    cIndex--;
+                }
+            }
+            counters.Add(new Counter(ch, k));
+        }
+        foreach (Counter curC in counters)
+            max = Math.Max(max, curC.ValidLength);
+        return max;
+    }
+
+    private class Counter
+    {
+        public int Length { get; private set; }
+        public bool IsValid => _maxMisses >= Length- _maxCount;
+        public int ValidLength => _maxCount + Math.Min(Length- _maxCount, _maxMisses);
+        private int[] _letters = new int[26];
+        private int _maxCount => _letters[_maxLetter-65];
+        private char _maxLetter;
+        private readonly int _maxMisses;
+
+        public Counter(char ch, int k)
+        {
+            _maxMisses = k;
+            Length = 1;
+            _letters[ch - 65] = 1;
+            _maxLetter = ch;
+        }
+
+        public void Add(char ch)
+        {
+            _letters[ch - 65]+=1;
+            if (_letters[ch - 65] > _maxCount)
+                _maxLetter = ch;
+            Length++;
+        }
+    }
+}