Merge pull request TheAlgorithms#1461 from shellhub/master

Created Problem06 in Project Euler

Author: realDuYuanChao

DIRECTORY.md

@@ -204,6 +204,7 @@
   * [Problem01](https://github.com/TheAlgorithms/Java/blob/master/ProjectEuler/Problem01.java)
   * [Problem02](https://github.com/TheAlgorithms/Java/blob/master/ProjectEuler/Problem02.java)
   * [Problem04](https://github.com/TheAlgorithms/Java/blob/master/ProjectEuler/Problem04.java)
+  * [Problem06](https://github.com/TheAlgorithms/Java/blob/master/ProjectEuler/Problem06.java)
 
 ## Searches
   * [BinarySearch](https://github.com/TheAlgorithms/Java/blob/master/Searches/BinarySearch.java)

ProjectEuler/Problem06.java

@@ -0,0 +1,46 @@
+package ProjectEuler;
+
+/**
+ * The sum of the squares of the first ten natural numbers is,
+ * 1^2 + 2^2 + ... + 10^2 = 385
+ * The square of the sum of the first ten natural numbers is,
+ * (1 + 2 + ... + 10)^2 = 552 = 3025
+ * Hence the difference between the sum of the squares of the first ten natural
+ * numbers and the square of the sum is 3025 − 385 = 2640.
+ * Find the difference between the sum of the squares of the first N natural
+ * numbers and the square of the sum.
+ * <p>
+ * link: https://projecteuler.net/problem=6
+ */
+public class Problem06 {
+    public static void main(String[] args) {
+        int[][] testNumbers = {
+                {10, 2640},
+                {15, 13160},
+                {20, 41230},
+                {50, 1582700}
+        };
+
+        for (int[] testNumber : testNumbers) {
+            assert solution1(testNumber[0]) == testNumber[1]
+                    && solutions2(testNumber[0]) == testNumber[1];
+        }
+    }
+
+    private static int solution1(int n) {
+        int sum1 = 0;
+        int sum2 = 0;
+        for (int i = 1; i <= n; ++i) {
+            sum1 += i * i;
+            sum2 += i;
+        }
+        return sum2 * sum2 - sum1;
+    }
+
+
+    private static int solutions2(int n) {
+        int sumOfSquares = n * (n + 1) * (2 * n + 1) / 6;
+        int squareOfSum = (int) Math.pow((n * (n + 1) / 2.0), 2);
+        return squareOfSum - sumOfSquares;
+    }
+}