Data commit

Task/Truncatable-primes/Rust/truncatable-primes.rust

@@ -0,0 +1,71 @@
+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 is_left_truncatable(p: u32) -> bool {
+    let mut n = 10;
+    let mut q = p;
+    while p > n {
+        if !is_prime(p % n) || q == p % n {
+            return false;
+        }
+        q = p % n;
+        n *= 10;
+    }
+    true
+}
+
+fn is_right_truncatable(p: u32) -> bool {
+    let mut q = p / 10;
+    while q > 0 {
+        if !is_prime(q) {
+            return false;
+        }
+        q /= 10;
+    }
+    true
+}
+
+fn main() {
+    let limit = 1000000;
+    let mut largest_left = 0;
+    let mut largest_right = 0;
+    let mut p = limit;
+    while p >= 2 {
+        if is_prime(p) && is_left_truncatable(p) {
+            largest_left = p;
+            break;
+        }
+        p -= 1;
+    }
+    println!("Largest left truncatable prime is {}", largest_left);
+    p = limit;
+    while p >= 2 {
+        if is_prime(p) && is_right_truncatable(p) {
+            largest_right = p;
+            break;
+        }
+        p -= 1;
+    }
+    println!("Largest right truncatable prime is {}", largest_right);
+}