prob28: solved

src/bin/prob28.rs

@@ -0,0 +1,27 @@
+// Number Spiral Diagonals
+
+trait Math {
+    fn arithmetic_sum(self) -> usize;
+}
+
+impl Math for usize {
+    fn arithmetic_sum(self) -> usize {
+        8 * self * (self + 1) * (2 * self + 1) / 3 + 2 * self * (self + 1) + 4 * self + 1
+    }
+}
+
+fn spiral_diagonals_sum(length: usize) -> usize {
+    assert!(length % 2 != 0, "The length of matrix must be odd!");
+
+    (length / 2).arithmetic_sum()
+}
+
+pj_euler::run!("Number Spiral Diagonals", spiral_diagonals_sum(1001));
+
+pj_euler::test!(
+    number_spiral_diagonals{
+        {sum_spiral_diagonals_of_3x3_matrix, spiral_diagonals_sum(3), 25},
+        {sum_spiral_diagonals_of_5x5_matrix, spiral_diagonals_sum(5), 101},
+        {sum_spiral_diagonals_of_7x7_matrix, spiral_diagonals_sum(7), 261},
+    }
+);