diff --git a/src/llm_benchmark/control/double.py b/src/llm_benchmark/control/double.py
index 4be41d7..789c280 100644
--- a/src/llm_benchmark/control/double.py
+++ b/src/llm_benchmark/control/double.py
@@ -1,4 +1,4 @@
-from typing import List
+from typing import List, Tuple
 
 
 class DoubleForLoop:
@@ -12,12 +12,7 @@ def sum_square(n: int) -> int:
         Returns:
             int: Sum of squares of numbers from 0 to n
         """
-        sum_ = 0
-        for i in range(n):
-            for j in range(n):
-                if i == j:
-                    sum_ += i * j
-        return sum_
+        return n * (n - 1) * (2 * n - 1) // 6
 
     @staticmethod
     def sum_triangle(n: int) -> int:
@@ -29,11 +24,7 @@ def sum_triangle(n: int) -> int:
         Returns:
             int: Sum of triangle of numbers from 0 to n
         """
-        sum_ = 0
-        for i in range(n):
-            for j in range(i + 1):
-                sum_ += j
-        return sum_
+        return n * (n + 1) * (n - 1) // 6
 
     @staticmethod
     def count_pairs(arr: List[int]) -> int:
@@ -47,16 +38,14 @@ def count_pairs(arr: List[int]) -> int:
         Returns:
             int: Number of pairs in the array
         """
-        count = 0
-        for i in range(len(arr)):
-            ndup = 0
-            for j in range(len(arr)):
-                if arr[i] == arr[j]:
-                    ndup += 1
-            if ndup == 2:
-                count += 1
-
-        return count // 2
+        counts = {}
+        for x in arr:
+            counts[x] = counts.get(x, 0) + 1
+        
+        pairs = 0
+        for count in counts.values():
+            pairs += count // 2
+        return pairs
 
     @staticmethod
     def count_duplicates(arr0: List[int], arr1: List[int]) -> int:
@@ -69,12 +58,9 @@ def count_duplicates(arr0: List[int], arr1: List[int]) -> int:
         Returns:
             int: Number of duplicates between the two arrays
         """
-        count = 0
-        for i in range(len(arr0)):
-            for j in range(len(arr1)):
-                if i == j and arr0[i] == arr1[j]:
-                    count += 1
-        return count
+        set0 = set(arr0)
+        set1 = set(arr1)
+        return len(set0.intersection(set1))
 
     @staticmethod
     def sum_matrix(m: List[List[int]]) -> int:
@@ -87,7 +73,7 @@ def sum_matrix(m: List[List[int]]) -> int:
             int: Sum of matrix of integers
         """
         sum_ = 0
-        for i in range(len(m)):
-            for j in range(len(m[i])):
-                sum_ += m[i][j]
+        for row in m:
+            for val in row:
+                sum_ += val
         return sum_