Solve Problem 28

src/main/java/net/projecteuler/problems/problems026to050/Problem028.java

@@ -0,0 +1,41 @@
+package net.projecteuler.problems.problems026to050;
+
+import java.util.HashSet;
+
+public class Problem028 {
+
+  public int solve() {
+    var count = 1001;
+    var numbers = numbersInLeftToRightDiagonal(count);
+    numbers.addAll(numbersInRightToLeftDiagonal(count));
+    return numbers.stream().mapToInt(Integer::intValue).sum();
+  }
+
+  private HashSet<Integer> numbersInRightToLeftDiagonal(int count) {
+    var current = 1;
+    var increment = 2;
+    var storage = new HashSet<Integer>();
+    storage.add(current);
+    for (int i = 0; i < count - 1; i++) {
+      current += increment;
+      increment += 2;
+      storage.add(current);
+    }
+    return storage;
+  }
+
+  private HashSet<Integer> numbersInLeftToRightDiagonal(int count) {
+    var current = 1;
+    var increment = 4;
+    var storage = new HashSet<Integer>();
+    storage.add(current);
+    for (int i = 0; i < (count / 2); i++) {
+      for (int k = 0; k < 2; k++) {
+        current += increment;
+        storage.add(current);
+      }
+      increment += 4;
+    }
+    return storage;
+  }
+}

src/test/java/net/projecteuler/problems/problems026to050/Problem028Test.java

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+package net.projecteuler.problems.problems026to050;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class Problem028Test {
+
+  @Test
+  void solve() {
+    assertEquals(669171001, new Problem028().solve());
+  }
+}