diff --git a/app/src/main/java/control/Double.java b/app/src/main/java/control/Double.java
index cc5cf15..ddf4908 100644
--- a/app/src/main/java/control/Double.java
+++ b/app/src/main/java/control/Double.java
@@ -1,5 +1,9 @@
 package control;
 
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Arrays;
+
 public class Double {
   /**
    * Sums all values squared from 0 to n
@@ -8,15 +12,8 @@ public class Double {
    * @return The sum of the first n natural numbers squared.
    */
   public static int sumSquare(int n) {
-    int sum = 0;
-    for (int i = 0; i < n; i++) {
-      for (int j = 0; j < n; j++) {
-        if (i == j) {
-          sum = sum + i * j;
-        }
-      }
-    }
-    return sum;
+    // Using the mathematical formula n(n+1)(2n+1)/6 for sum of squares
+    return n * (n + 1) * (2 * n + 1) / 6;
   }
 
   /**
@@ -26,13 +23,8 @@ public static int sumSquare(int n) {
    * @return The sum of the first n triangular numbers.
    */
   public static int sumTriangle(int n) {
-    int sum = 0;
-    for (int i = 0; i < n + 1; i++) {
-      for (int j = 0; j < i; j++) {
-        sum = sum + j;
-      }
-    }
-    return sum;
+    // Using the mathematical formula n(n+1)(n+2)/6 for sum of triangular numbers
+    return n * (n + 1) * (n + 2) / 6;
   }
 
   /**
@@ -44,19 +36,17 @@ public static int sumTriangle(int n) {
    * @return The number of pairs in the array.
    */
   public static int countPairs(int[] arr) {
-    int count = 0;
-    for (int i = 0; i < arr.length; i++) {
-      int nDuplicates = 0;
-      for (int j = 0; j < arr.length; j++) {
-        if (arr[i] == arr[j]) {
-          nDuplicates++;
-        }
-      }
-      if (nDuplicates == 2) {
-        count++;
+    Map<Integer, Integer> counts = new HashMap<>();
+    for (int value : arr) {
+      counts.put(value, counts.getOrDefault(value, 0) + 1);
+    }
+    int pairs = 0;
+    for (int count : counts.values()) {
+      if (count == 2) {
+        pairs++;
       }
     }
-    return count / 2;
+    return pairs;
   }
 
   /**
@@ -68,12 +58,14 @@ public static int countPairs(int[] arr) {
    *         equal.
    */
   public static int countDuplicates(int[] arr0, int[] arr1) {
+    if (arr0 == null || arr1 == null) {
+      return 0;
+    }
     int count = 0;
-    for (int i = 0; i < arr0.length; i++) {
-      for (int j = 0; j < arr1.length; j++) {
-        if (i == j && arr0[i] == arr1[j]) {
-          count++;
-        }
+    int minLength = Math.min(arr0.length, arr1.length);
+    for (int i = 0; i < minLength; i++) {
+      if (arr0[i] == arr1[i]) {
+        count++;
       }
     }
     return count;
@@ -88,13 +80,11 @@ public static int countDuplicates(int[] arr0, int[] arr1) {
    * @return The sum of all values in the 2D array.
    */
   public static int sumMatrix(int[][] arr) {
-    int sum = 0;
-    int n = arr.length;
-    for (int i = 0; i < n; i++) {
-      for (int j = 0; j < n; j++) {
-        sum += arr[i][j];
-      }
+    if (arr == null || arr.length == 0) {
+      return 0;
     }
-    return sum;
+    return Arrays.stream(arr)
+        .flatMapToInt(Arrays::stream)
+        .sum();
   }
-}
+}
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