Data commit

Task/Circular-primes/D/circular-primes.d

@@ -0,0 +1,97 @@
+import std.bigint;
+import std.stdio;
+
+immutable PRIMES = [
+    2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97,
+    101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199,
+    211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293,
+    307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397,
+    401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499,
+    503, 509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599,
+    601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691,
+    701, 709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797,
+    809, 811, 821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887,
+    907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997
+];
+
+bool isPrime(BigInt n) {
+    if (n < 2) {
+        return false;
+    }
+
+    foreach (p; PRIMES) {
+        if (n == p) {
+            return true;
+        }
+        if (n % p == 0) {
+            return false;
+        }
+        if (p * p > n) {
+            return true;
+        }
+    }
+
+    for (auto m = BigInt(PRIMES[$ - 1]); m * m <= n ; m += 2) {
+        if (n % m == 0) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+// e.g. returns 2341 if n = 1234
+BigInt cycle(BigInt n) {
+    BigInt m = n;
+    BigInt p = 1;
+    while (m >= 10) {
+        p *= 10;
+        m /= 10;
+    }
+    return m + 10 * (n % p);
+}
+
+bool isCircularPrime(BigInt p) {
+    if (!isPrime(p)) {
+        return false;
+    }
+    for (auto p2 = cycle(p); p2 != p; p2 = cycle(p2)) {
+        if (p2 < p || !isPrime(p2)) {
+            return false;
+        }
+    }
+    return true;
+}
+
+BigInt repUnit(int len) {
+    BigInt n = 0;
+    while (len > 0) {
+        n = 10 * n + 1;
+        len--;
+    }
+    return n;
+}
+
+void main() {
+    writeln("First 19 circular primes:");
+    int count = 0;
+    foreach (p; PRIMES) {
+        if (isCircularPrime(BigInt(p))) {
+            if (count > 0) {
+                write(", ");
+            }
+            write(p);
+            count++;
+        }
+    }
+    for (auto p = BigInt(PRIMES[$ - 1]) + 2; count < 19; p += 2) {
+        if (isCircularPrime(BigInt(p))) {
+            if (count > 0) {
+                write(", ");
+            }
+            write(p);
+            count++;
+        }
+    }
+    writeln;
+}