add 94 (WIP)

src/euler94/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "euler94"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

src/euler94/src/main.rs

@@ -0,0 +1,50 @@
+type Num = u64;
+
+const ONE_BILLION: Num = 1_000_000_000;
+
+fn main() {
+    let mut sum = 0 as Num;
+    'outer: for i in 2.. {
+        let a_b = i as Num;
+        for c in [a_b - 1, a_b + 1] {
+            let t = Triangle::new(a_b, c);
+            let p = t.perimeter();
+
+            if p > ONE_BILLION {
+                break 'outer;
+            }
+
+            if t.has_integer_area() {
+                sum += p;
+            }
+        }
+    }
+
+    println!("{sum}");
+}
+
+struct Triangle {
+    a_b: Num,
+    c: Num,
+}
+
+impl Triangle {
+    fn new(a_b: Num, c: Num) -> Self {
+        Self { a_b, c }
+    }
+
+    fn perimeter(&self) -> Num {
+        2 * self.a_b + self.c
+    }
+
+    fn has_integer_area(&self) -> bool {
+        let a_b = self.a_b as f64;
+        let c = self.c as f64;
+        let area = c / 4. * (4. * a_b.powi(2) - c.powi(2)).sqrt();
+        is_integer(area)
+    }
+}
+
+fn is_integer(x: f64) -> bool {
+    (x.round() - x).abs() <= f64::EPSILON
+}