[Hacker Rank]: Project Euler #1: Multiples of 3 and 5 solved ✓

Author: Gonzalo Diaz

algorithm-exercises-java/src/main/java/ae/hackerrank/projecteuler/Euler001.java

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+package ae.hackerrank.projecteuler;
+
+import java.text.MessageFormat;
+
+/**
+ * Multiples of 3 and 5.
+ *
+ * @link Problem definition [[docs/hackerrank/projecteuler/euler001.md]]
+ */
+public class Euler001 {
+
+  private Euler001() {}
+
+  static java.util.logging.Logger logger = ae.projecteuler.util.CustomLogger.getLogger();
+
+  /**
+   * Greatest common divisor
+   */
+  private static Long gcd(Integer a, Integer b) {
+    if (a == 0) {
+      return (long) b;
+    }
+
+    return gcd(b % a, a);
+  }
+
+  /**
+   * Sum of Arithmetic Progression series
+   */
+  private static Long sumAP(Long numberOfTerms, Long distance)
+  {
+    long n = numberOfTerms / distance;
+
+    return (long) ((n) * (1 + n) * distance / 2);
+  }
+
+  /**
+   * Multiples of 3 and 5.
+   */
+  public static Long euler001(Integer a, Integer b, Integer n) {
+    Long result = null;
+
+    n = n - 1;
+    Long lcm = (a * b) / gcd(a, b);
+
+    String log = MessageFormat.format("Problem 000XX solved: {0}", result);
+
+    result = sumAP((long) n, (long) a) + sumAP((long) n, (long) b) - sumAP((long) n, lcm);
+
+    logger.info(log);
+
+    return result;
+  }
+}
+
+//CHECKSTYLE.ON: JavadocParagraph

algorithm-exercises-java/src/test/java/ae/hackerrank/projecteuler/Euler001Test.java

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+package ae.hackerrank.projecteuler;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+
+class Euler001Test {
+
+  @ParameterizedTest
+  @CsvSource({
+      "3, 5, 10, 23, Test Case 1",
+      "3, 5, 100, 2318, Test Case 2",
+      "3, 5, 1000, 233168, Test Case 3"
+  })
+  void euler001(
+      int a,
+      int b,
+      int n,
+      long answer,
+      String testCase) {
+
+    Long solutionFound = Euler001.euler001(a, b, n);
+
+    String log = String.format("Problem 0023 {0} answer must be: {1}", testCase, answer);
+    assertEquals(answer, solutionFound, log);
+  }
+}

docs/hackerrank/projecteuler/euler001.md

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+# [Multiples of 3 and 5](https://www.hackerrank.com/contests/projecteuler/challenges/euler001)
+
+- Difficulty: #easy
+- Category: #ProjectEuler+
+
+If we list all the natural numbers below $ 10 $ that are multiples of
+ $ 3 $ or $ 5 $, we get $ 3, 5, 6 $ and $ 9 $.
+ The sum of these multiples
+ is $ 23 $.
+
+Find the sum of all the multiples of $ 3 $ or $ 5 $ below $ N $.
+
+## Input Format
+
+First line contains $ T $ that denotes the number of test cases.
+This is followed by $ T $ lines, each containing an integer, $ N $.
+
+## Constraints
+
+- 1 $ \leq T \leq 10^5 $
+- 1 $ \leq N \leq 10^9 $
+
+## Output Format
+
+For each test case, print an integer that denotes the sum of all the multiples
+of $ 3 $ or $ 5 $ below $ N $.
+
+## Sample Input 0
+
+```text
+2
+10
+100
+```
+
+## Sample Output 0
+
+```text
+23
+2318
+```
+
+## Explanation 0
+
+For $ N = 10 $, if we list all the natural numbers below $ 10 $ that are
+ multiples of $ 3 $ or $ 5 $, we get $ 3, 5, 6 $ and $ 9 $.
+  The sum of these multiples is $ 23 $.
+
+Similarly for $ N = 100 $, we get $ 2318 $.