Refactor c/difference-of-squares

Curious to benchmark the different approaches.

c/difference-of-squares/src/difference_of_squares.c

@@ -1,16 +1,17 @@
 #include <stdio.h>
 
+// The sum of the first N natural numbers can be calculated as
+// N * (N + 1) / 2. To get the square, we multiply the sum with itself.
+// This formula saves us from having to loop up to N.
 int square_of_sum(int n) {
-	int sum = (n * (n + 1)) / 2;
-	return sum * sum;
+	return ((n * (n + 1)) / 2) * ((n * (n + 1)) / 2);
 }
 
+// The sum of the squares of the first N natural numbers can be
+// calculated as (n * (n + 1) * ((2 * n) + 1)) / 6.
+// This formula saves us from having to loop up to N.
 int sum_of_squares(int n) {
-	int sum = 0;
-
-	for (int i = 1; i <= n; i++) sum += i * i;
-
-	return sum;
+	return (n * (n + 1) * ((2 * n) + 1)) / 6;
 }
 
 int difference_of_squares(int n) {