optimize 94

src/euler94/src/main.rs

@@ -1,34 +1,32 @@
-use f128::f128;
-use num_traits::Float;
-
-type Num = f128;
-
-static mut ONE_BILLION: Num = f128::ZERO;
-const ONE: Num = f128::ONE;
+type Num = usize;
 
 fn main() {
-    unsafe {
-        ONE_BILLION = f128::from(1_000_000_000.);
+    let mut sum = 0;
+
+    let mut i = 5;
+    'outer: loop {
+        if i > 333_333_334 {
+            break;
+        }
+        let a = i;
+
+        if a % 2 == 0 {
+            i += 1;
+            continue;
         }
 
-    let mut sum = f128::ZERO;
-
-    'outer: for i in 2.. {
-        let a = f128::from(i);
-
-        for c in [a - ONE, a + ONE] {
+        for c in [a - 1, a + 1] {
             let t = Triangle::new(a, c);
-            let p = t.perimeter();
-
-            if unsafe { p > ONE_BILLION } {
-                break 'outer;
-            }
 
             if t.has_integer_area() {
                 println!("{:.10}, {:.10}", t.a, t.c);
-                sum += p;
+                sum += t.perimeter();
+                i = ((i as f64) * 3.59).trunc() as usize;
+                continue 'outer;
             }
         }
+
+        i += 1;
     }
 
     println!("{sum:.15}");
@@ -45,21 +43,13 @@ impl Triangle {
     }
 
     fn perimeter(&self) -> Num {
-        Num::TWO * self.a + self.c
+        2 * self.a + self.c
     }
 
     fn has_integer_area(&self) -> bool {
-        is_integer(self.area())
-    }
+        let h = 4 * self.a.pow(2) - self.c.pow(2);
+        let root = (h as f64).sqrt().trunc() as usize;
 
-    fn area(&self) -> Num {
-        let a = self.a;
-        let c = self.c;
-
-        c / Num::from(4.) * (Num::from(4.) * a.powi(2) - c.powi(2)).sqrt()
+        root * root == h
     }
 }
-
-fn is_integer(x: Num) -> bool {
-    (x.round() - x).abs() <= Num::EPSILON
-}