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src/euler44/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "euler44"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+itertools = "0.14.0"

src/euler44/src/main.rs

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+use itertools::Itertools;
+
+fn main() {
+    let pentagonals: Vec<_> = (1..10000).map(pentagonal_number).collect();
+    let combinations: Vec<_> = pentagonals.iter().combinations(2).collect();
+
+    for item in combinations {
+        let smaller = *item.first().unwrap();
+        let larger = *item.get(1).unwrap();
+        let sum = smaller + larger;
+        let difference = larger - smaller;
+        if pentagonals.contains(&sum) && pentagonals.contains(&difference) {
+            println!("{difference}");
+            break;
+        }
+    }
+}
+
+fn pentagonal_number(n: usize) -> usize {
+    n * (3 * n - 1) / 2
+}