Data commit

Task/Smarandache-prime-digital-sequence/Rust/smarandache-prime-digital-sequence.rust

@@ -0,0 +1,73 @@
+fn is_prime(n: u32) -> bool {
+    if n < 2 {
+        return false;
+    }
+    if n % 2 == 0 {
+        return n == 2;
+    }
+    if n % 3 == 0 {
+        return n == 3;
+    }
+    if n % 5 == 0 {
+        return n == 5;
+    }
+    let mut p = 7;
+    const WHEEL: [u32; 8] = [4, 2, 4, 2, 4, 6, 2, 6];
+    loop {
+        for w in &WHEEL {
+            if p * p > n {
+                return true;
+            }
+            if n % p == 0 {
+                return false;
+            }
+            p += w;
+        }
+    }
+}
+
+fn next_prime_digit_number(n: u32) -> u32 {
+    if n == 0 {
+        return 2;
+    }
+    match n % 10 {
+        2 => n + 1,
+        3 | 5 => n + 2,
+        _ => 2 + next_prime_digit_number(n / 10) * 10,
+    }
+}
+
+fn smarandache_prime_digital_sequence() -> impl std::iter::Iterator<Item = u32> {
+    let mut n = 0;
+    std::iter::from_fn(move || {
+        loop {
+            n = next_prime_digit_number(n);
+            if is_prime(n) {
+                break;
+            }
+        }
+        Some(n)
+    })
+}
+
+fn main() {
+    let limit = 1000000000;
+    let mut seq = smarandache_prime_digital_sequence().take_while(|x| *x < limit);
+    println!("First 25 SPDS primes:");
+    for i in seq.by_ref().take(25) {
+        print!("{} ", i);
+    }
+    println!();
+    if let Some(p) = seq.by_ref().nth(99 - 25) {
+        println!("100th SPDS prime: {}", p);
+    }
+    if let Some(p) = seq.by_ref().nth(999 - 100) {
+        println!("1000th SPDS prime: {}", p);
+    }
+    if let Some(p) = seq.by_ref().nth(9999 - 1000) {
+        println!("10,000th SPDS prime: {}", p);
+    }
+    if let Some(p) = seq.last() {
+        println!("Largest SPDS prime less than {}: {}", limit, p);
+    }
+}