Task: Brazilian numbers



C#: using System;
class Program {
 
  static bool sameDigits(int n, int b) {
    int f = n % b;
    while ((n /= b) > 0) if (n % b != f) return false;
    return true;
  }
 
  static bool isBrazilian(int n) {
    if (n < 7) return false;
    if (n % 2 == 0) return true;
    for (int b = 2; b < n - 1; b++) if (sameDigits(n, b)) return true;
    return false;
  }
 
  static bool isPrime(int n) {
    if (n < 2) return false;
    if (n % 2 == 0) return n == 2;
    if (n % 3 == 0) return n == 3;
    int d = 5;
    while (d * d <= n) {
      if (n % d == 0) return false; d += 2;
      if (n % d == 0) return false; d += 4;
    }
    return true;
  }
 
  static void Main(string[] args) {
    foreach (string kind in ",odd ,prime ".Split(',')) {
      bool quiet = false; int BigLim = 99999, limit = 20;
      Console.WriteLine("First {0} {1}Brazilian numbers:", limit, kind);
      int c = 0, n = 7;
      while (c < BigLim) {
        if (isBrazilian(n)) {
          if (!quiet) Console.Write("{0:n0} ", n);
          if (++c == limit) { Console.Write("\n\n"); quiet = true; }
        }
        if (quiet && kind != "") continue;
        switch (kind) {
          case "": n++; break;
          case "odd ": n += 2; break;
          case "prime ":
            while (true) {
              n += 2;
              if (isPrime(n)) break;
            } break;
        }
      }
      if (kind == "") Console.WriteLine("The {0:n0}th Brazilian number is: {1:n0}\n", BigLim + 1, n);
    }
  }
}



Java: import java.math.BigInteger;
import java.util.List;

public class Brazilian {
    private static final List<Integer> primeList = List.of(
        2, 3, 5, 7, 9, 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, 169, 173, 179, 181,
        191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 247, 251, 257, 263, 269, 271, 277, 281,
        283, 293, 299, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 377, 379, 383, 389,
        397, 401, 403, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 481, 487, 491,
        499, 503, 509, 521, 523, 533, 541, 547, 557, 559, 563, 569, 571, 577, 587, 593, 599, 601, 607,
        611, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 689, 691, 701, 709, 719,
        727, 733, 739, 743, 751, 757, 761, 767, 769, 773, 787, 793, 797, 809, 811, 821, 823, 827, 829,
        839, 853, 857, 859, 863, 871, 877, 881, 883, 887, 907, 911, 919, 923, 929, 937, 941, 947, 949,
        953, 967, 971, 977, 983, 991, 997
    );

    public static boolean isPrime(int n) {
        if (n < 2) {
            return false;
        }

        for (Integer prime : primeList) {
            if (n == prime) {
                return true;
            }
            if (n % prime == 0) {
                return false;
            }
            if (prime * prime > n) {
                return true;
            }
        }

        BigInteger bi = BigInteger.valueOf(n);
        return bi.isProbablePrime(10);
    }

    private static boolean sameDigits(int n, int b) {
        int f = n % b;
        while ((n /= b) > 0) {
            if (n % b != f) {
                return false;
            }
        }
        return true;
    }

    private static boolean isBrazilian(int n) {
        if (n < 7) return false;
        if (n % 2 == 0) return true;
        for (int b = 2; b < n - 1; ++b) {
            if (sameDigits(n, b)) {
                return true;
            }
        }
        return false;
    }

    public static void main(String[] args) {
        for (String kind : List.of("", "odd ", "prime ")) {
            boolean quiet = false;
            int bigLim = 99_999;
            int limit = 20;
            System.out.printf("First %d %sBrazilian numbers:\n", limit, kind);
            int c = 0;
            int n = 7;
            while (c < bigLim) {
                if (isBrazilian(n)) {
                    if (!quiet) System.out.printf("%d ", n);
                    if (++c == limit) {
                        System.out.println("\n");
                        quiet = true;
                    }
                }
                if (quiet && !"".equals(kind)) continue;
                switch (kind) {
                    case "":
                        n++;
                        break;
                    case "odd ":
                        n += 2;
                        break;
                    case "prime ":
                        do {
                            n += 2;
                        } while (!isPrime(n));
                        break;
                    default:
                        throw new AssertionError("Oops");
                }
            }
            if ("".equals(kind)) {
                System.out.printf("The %dth Brazilian number is: %d\n\n", bigLim + 1, n);
            }
        }
    }
}