fast solution 451

451. Sort Characters By Frequency/Fast/FastSolution.cs

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+using System.Text;
+
+namespace _451._Sort_Characters_By_Frequency.Fast;
+
+public class Solution
+{
+    private static int Comparer((char, int) el1, (char, int) el2)
+    {
+        return el2.Item2.CompareTo(el1.Item2);
+    }
+    
+    public string FrequencySort(string s)
+    {
+        var count = new (char, int)[128];
+        for (var ch = (char)0; ch < count.Length; ch++)
+            count[ch].Item1 = ch;
+        foreach (var c in s)
+            count[c].Item2++;
+        var sb = new StringBuilder();
+        Array.Sort(count, Comparer);
+        for (var ch = (char)0; ch < count.Length; ch++)
+            while (count[ch].Item2-- > 0)
+                sb.Append(count[ch].Item1);
+        return sb.ToString();
+    }
+}