Task: Brazilian numbers




Go: package main

import "fmt"

func sameDigits(n, b int) bool {
    f := n % b
    n /= b
    for n > 0 {
        if n%b != f {
            return false
        }
        n /= b
    }
    return true
}

func isBrazilian(n int) bool {
    if n < 7 {
        return false
    }
    if n%2 == 0 && n >= 8 {
        return true
    }
    for b := 2; b < n-1; b++ {
        if sameDigits(n, b) {
            return true
        }
    }
    return false
}

func isPrime(n int) bool {
    switch {
    case n < 2:
        return false
    case n%2 == 0:
        return n == 2
    case n%3 == 0:
        return n == 3
    default:
        d := 5
        for d*d <= n {
            if n%d == 0 {
                return false
            }
            d += 2
            if n%d == 0 {
                return false
            }
            d += 4
        }
        return true
    }
}

func main() {
    kinds := []string{" ", " odd ", " prime "}
    for _, kind := range kinds {
        fmt.Printf("First 20%sBrazilian numbers:\n", kind)
        c := 0
        n := 7
        for {
            if isBrazilian(n) {
                fmt.Printf("%d ", n)
                c++
                if c == 20 {
                    fmt.Println("\n")
                    break
                }
            }
            switch kind {
            case " ":
                n++
            case " odd ":
                n += 2
            case " prime ":
                for {
                    n += 2
                    if isPrime(n) {
                        break
                    }
                }
            }
        }
    }

    n := 7
    for c := 0; c < 100000; n++ {
        if isBrazilian(n) {
            c++
        }
    }
    fmt.Println("The 100,000th Brazilian number:", n-1)
}


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);
            }
        }
    }
}