Task: Humble numbers




Go: package main

import (
    "fmt"
    "math/big"
)

var (
    one   = new(big.Int).SetUint64(1)
    two   = new(big.Int).SetUint64(2)
    three = new(big.Int).SetUint64(3)
    five  = new(big.Int).SetUint64(5)
    seven = new(big.Int).SetUint64(7)
    ten   = new(big.Int).SetUint64(10)
)

func min(a, b *big.Int) *big.Int {
    if a.Cmp(b) < 0 {
        return a
    }
    return b
}

func humble(n int) []*big.Int {
    h := make([]*big.Int, n)
    h[0] = new(big.Int).Set(one)
    next2, next3 := new(big.Int).Set(two), new(big.Int).Set(three)
    next5, next7 := new(big.Int).Set(five), new(big.Int).Set(seven)
    var i, j, k, l int
    for m := 1; m < len(h); m++ {
        h[m] = new(big.Int).Set(min(next2, min(next3, min(next5, next7))))
        if h[m].Cmp(next2) == 0 {
            i++
            next2.Mul(two, h[i])
        }
        if h[m].Cmp(next3) == 0 {
            j++
            next3.Mul(three, h[j])
        }
        if h[m].Cmp(next5) == 0 {
            k++
            next5.Mul(five, h[k])
        }
        if h[m].Cmp(next7) == 0 {
            l++
            next7.Mul(seven, h[l])
        }
    }
    return h
}

func commatize(n int) string {
    s := fmt.Sprintf("%d", n)
    le := len(s)
    for i := le - 3; i >= 1; i -= 3 {
        s = s[0:i] + "," + s[i:]
    }
    return s
}

func main() {
    const n = 13 * 1e6  
    h := humble(n) 
    fmt.Println("The first 50 humble numbers are:")
    fmt.Println(h[0:50])

    maxDigits := len(h[len(h)-1].String()) - 1
    counts := make([]int, maxDigits+1)
    var maxUsed int
    digits := 1
    pow10 := new(big.Int).Set(ten)
    for i := 0; i < len(h); i++ {
        for {
            if h[i].Cmp(pow10) >= 0 {
                pow10.Mul(pow10, ten)
                digits++
            } else {
                break
            }
        }  
        if digits > maxDigits {
            maxUsed = i
            break
        }
        counts[digits]++
    }
    fmt.Printf("\nOf the first %s humble numbers:\n", commatize(maxUsed))
    for i := 1; i <= maxDigits; i++ {
        s := "s"
        if i == 1 {
            s = ""
        }
        fmt.Printf("%9s have %2d digit%s\n", commatize(counts[i]), i, s)
    }       
}


Java: import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class HumbleNumbers {

    public static void main(String[] args) {
        System.out.println("First 50 humble numbers:");
        System.out.println(Arrays.toString(humble(50)));
        Map<Integer,Integer> lengthCountMap = new HashMap<>();
        BigInteger[] seq = humble(1_000_000);
        for ( int i = 0 ; i < seq.length ; i++ ) {
            BigInteger humbleNumber = seq[i];
            int len = humbleNumber.toString().length();
            lengthCountMap.merge(len, 1, (v1, v2) -> v1 + v2);
        }
        List<Integer> sorted = new ArrayList<>(lengthCountMap.keySet());
        Collections.sort(sorted);
        System.out.printf("Length  Count%n");
        for ( Integer len : sorted ) {
            System.out.printf("    %2s  %5s%n", len, lengthCountMap.get(len));
        }
    }
    
    private static BigInteger[] humble(int n) {
        BigInteger two = BigInteger.valueOf(2);
        BigInteger twoTest = two;
        BigInteger three = BigInteger.valueOf(3);
        BigInteger threeTest = three;
        BigInteger five = BigInteger.valueOf(5);
        BigInteger fiveTest = five;
        BigInteger seven = BigInteger.valueOf(7);
        BigInteger sevenTest = seven;
        BigInteger[] results = new BigInteger[n];
        results[0] = BigInteger.ONE;
        int twoIndex = 0, threeIndex = 0, fiveIndex = 0, sevenIndex = 0;
        for ( int index = 1 ; index < n ; index++ ) {
            results[index] = twoTest.min(threeTest).min(fiveTest).min(sevenTest);
            if ( results[index].compareTo(twoTest) == 0 ) {
                twoIndex++;
                twoTest = two.multiply(results[twoIndex]);
            }
            if (results[index].compareTo(threeTest) == 0 ) {
                threeIndex++;
                threeTest = three.multiply(results[threeIndex]);
            }
            if (results[index].compareTo(fiveTest) == 0 ) {
                fiveIndex++;
                fiveTest = five.multiply(results[fiveIndex]);
            }
            if (results[index].compareTo(sevenTest) == 0 ) {
                sevenIndex++;
                sevenTest = seven.multiply(results[sevenIndex]);
            }
        }
        return results;
    }

}