Finished projecteuler 087 quite quickly

projecteuler/087/src/main.rs

@@ -0,0 +1,62 @@
+use std::collections::HashSet;
+use std::time::Instant;
+
+fn primes(max_prime: u32) -> Vec<u32> {
+    let mut prime_bools = vec![true; max_prime as usize];
+    prime_bools[0] = false;
+    prime_bools[1] = false;
+
+    for p in 2..=(max_prime as f32).powf(0.5) as usize + 1 {
+        if !prime_bools[p] {
+            continue;
+        }
+
+        let mut i = p;
+        while i + p < max_prime as usize {
+            i += p;
+            prime_bools[i] = false;
+        }
+    }
+
+    prime_bools
+        .into_iter()
+        .enumerate()
+        .filter_map(|(n, b)| match b {
+            false => None,
+            true => Some(n as u32),
+        })
+        .collect()
+}
+
+fn main() {
+    println!("Hello, this is Patrick!");
+    let now = Instant::now();
+
+    let mut prime_power_triples = HashSet::new();
+    let max_value = 50000000;
+
+    let primes_power_two = primes(f32::powf(max_value as f32, 0.5) as u32 + 1);
+    let primes_power_three = primes(f32::powf(max_value as f32, 1.0 / 3.0) as u32 + 1);
+    let primes_power_four = primes(f32::powf(max_value as f32, 0.25) as u32 + 1);
+
+    for twos in primes_power_two.iter() {
+        for threes in primes_power_three.iter() {
+            for fours in primes_power_four.iter() {
+                let n = twos * twos + threes * threes * threes + fours * fours * fours * fours;
+                if n < max_value {
+                    prime_power_triples.insert(n);
+                }
+            }
+        }
+    }
+
+    println!(
+        "Number of prime power triples under {}: {:?}",
+        max_value,
+        prime_power_triples.len()
+    );
+
+    // println!("They are: {:?}", prime_power_triples);
+
+    println!("Time passed: {:?}", Instant::now() - now);
+}