Merge pull request #3185 from Dalton-V/main

Added 0187-repeated-dna-sequences.cs

Author: MHamiid

csharp/0187-repeated-dna-sequences.cs

@@ -0,0 +1,18 @@
+public class Solution
+{
+    public IList<string> FindRepeatedDnaSequences(string s)
+    {
+        var seen = new HashSet<string>();
+        var result = new HashSet<string>();
+
+        for (var i = 0; i < s.Length - 9; i++)
+        {
+            var cur = s.Substring(i, 10);
+            if (seen.Contains(cur))
+                result.Add(cur);
+            seen.Add(cur);
+        }
+
+        return result.ToList();
+    }
+}