Data commit

Task/Circular-primes/Rust/circular-primes.rust

@@ -0,0 +1,106 @@
+// [dependencies]
+// rug = "1.8"
+
+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;
+    }
+    let mut p = 5;
+    while p * p <= n {
+        if n % p == 0 {
+            return false;
+        }
+        p += 2;
+        if n % p == 0 {
+            return false;
+        }
+        p += 4;
+    }
+    true
+}
+
+fn cycle(n: u32) -> u32 {
+    let mut m: u32 = n;
+    let mut p: u32 = 1;
+    while m >= 10 {
+        p *= 10;
+        m /= 10;
+    }
+    m + 10 * (n % p)
+}
+
+fn is_circular_prime(p: u32) -> bool {
+    if !is_prime(p) {
+        return false;
+    }
+    let mut p2: u32 = cycle(p);
+    while p2 != p {
+        if p2 < p || !is_prime(p2) {
+            return false;
+        }
+        p2 = cycle(p2);
+    }
+    true
+}
+
+fn test_repunit(digits: usize) {
+    use rug::{integer::IsPrime, Integer};
+    let repunit = "1".repeat(digits);
+    let bignum = Integer::from_str_radix(&repunit, 10).unwrap();
+    if bignum.is_probably_prime(10) != IsPrime::No {
+        println!("R({}) is probably prime.", digits);
+    } else {
+        println!("R({}) is not prime.", digits);
+    }
+}
+
+fn main() {
+    use rug::{integer::IsPrime, Integer};
+    println!("First 19 circular primes:");
+    let mut count = 0;
+    let mut p: u32 = 2;
+    while count < 19 {
+        if is_circular_prime(p) {
+            if count > 0 {
+                print!(", ");
+            }
+            print!("{}", p);
+            count += 1;
+        }
+        p += 1;
+    }
+    println!();
+    println!("Next 4 circular primes:");
+    let mut repunit: u32 = 1;
+    let mut digits: usize = 1;
+    while repunit < p {
+        repunit = 10 * repunit + 1;
+        digits += 1;
+    }
+    let mut bignum = Integer::from(repunit);
+    count = 0;
+    while count < 4 {
+        if bignum.is_probably_prime(15) != IsPrime::No {
+            if count > 0 {
+                print!(", ");
+            }
+            print!("R({})", digits);
+            count += 1;
+        }
+        digits += 1;
+        bignum = bignum * 10 + 1;
+    }
+    println!();
+    test_repunit(5003);
+    test_repunit(9887);
+    test_repunit(15073);
+    test_repunit(25031);
+    test_repunit(35317);
+    test_repunit(49081);
+}