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src/euler28/Cargo.toml

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+[package]
+name = "euler28"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

src/euler28/src/main.rs

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+fn main() {
+    let result = spiral(1001);
+    println!("{result}");
+}
+
+fn spiral(edge_length: usize) -> usize {
+    let max = edge_length * edge_length;
+    let mut sum = 1;
+    let mut number = 1;
+    let mut offset = 2;
+    let steps = 4;
+    loop {
+        for _ in 0..steps {
+            number += offset;
+            sum += number;
+        }
+        offset += 2;
+        if number == max {
+            break;
+        }
+    }
+
+    sum
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::spiral;
+
+    #[test]
+    fn spiral_5() {
+        assert_eq!(spiral(5), 101);
+    }
+}