Task: Weird numbers



C#: using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace WeirdNumbers {
    class Program {
        static List<int> Divisors(int n) {
            List<int> divs = new List<int> { 1 };
            List<int> divs2 = new List<int>();

            for (int i = 2; i * i <= n; i++) {
                if (n % i == 0) {
                    int j = n / i;
                    divs.Add(i);
                    if (i != j) {
                        divs2.Add(j);
                    }
                }
            }

            divs.Reverse();
            divs2.AddRange(divs);
            return divs2;
        }

        static bool Abundant(int n, List<int> divs) {
            return divs.Sum() > n;
        }

        static bool Semiperfect(int n, List<int> divs) {
            if (divs.Count > 0) {
                var h = divs[0];
                var t = divs.Skip(1).ToList();
                if (n < h) {
                    return Semiperfect(n, t);
                } else {
                    return n == h
                        || Semiperfect(n - h, t)
                        || Semiperfect(n, t);
                }
            } else {
                return false;
            }
        }

        static List<bool> Sieve(int limit) {
            
            
            bool[] w = new bool[limit];
            for (int i = 2; i < limit; i += 2) {
                if (w[i]) continue;
                var divs = Divisors(i);
                if (!Abundant(i, divs)) {
                    w[i] = true;
                } else if (Semiperfect(i, divs)) {
                    for (int j = i; j < limit; j += i) {
                        w[j] = true;
                    }
                }
            }
            return w.ToList();
        }

        static void Main() {
            var w = Sieve(17_000);
            int count = 0;
            int max = 25;
            Console.WriteLine("The first 25 weird numbers:");
            for (int n = 2; count < max; n += 2) {
                if (!w[n]) {
                    Console.Write("{0} ", n);
                    count++;
                }
            }
            Console.WriteLine();
        }
    }
}



Java: import java.util.ArrayList;
import java.util.List;

public class WeirdNumbers {

    public static void main(String[] args) {
        int n = 2;
        
        for ( int count = 1 ; count <= 25 ; n += 2 ) {
            if ( isWeird(n) ) {
                System.out.printf("w(%d) = %d%n", count, n);
                count++;
            }
        }
    }
    
    private static boolean isWeird(int n) {
        List<Integer> properDivisors = getProperDivisors(n);
        return isAbundant(properDivisors, n) && ! isSemiPerfect(properDivisors, n);
    }
    
    private static boolean isAbundant(List<Integer> divisors, int n) {
        int divisorSum = divisors.stream().mapToInt(i -> i.intValue()).sum();
        return divisorSum > n;
    }
    
    
    private static boolean isSemiPerfect(List<Integer> divisors, int sum) {
        int size = divisors.size();
        
        
        boolean subset[][] = new boolean[sum+1][size+1];

        
        for (int i = 0; i <= size; i++) {
            subset[0][i] = true; 
        }
        
        
        for (int i = 1; i <= sum; i++) {
            subset[i][0] = false; 
        }
        
        
        for ( int i = 1 ; i <= sum ; i++ ) {
            for ( int j = 1 ; j <= size ; j++ ) {
                subset[i][j] = subset[i][j-1];
                int test = divisors.get(j-1);
                if ( i >= test ) {
                    subset[i][j] = subset[i][j] || subset[i - test][j-1]; 
                }
            } 
        } 

        return subset[sum][size];
    }

    private static final List<Integer> getProperDivisors(int number) {
        List<Integer> divisors = new ArrayList<Integer>();
        long sqrt = (long) Math.sqrt(number);
        for ( int i = 1 ; i <= sqrt ; i++ ) {
            if ( number % i == 0 ) {
                divisors.add(i);
                int div = number / i;
                if ( div != i && div != number ) {
                    divisors.add(div);
                }
            }
        }
        return divisors;
    }

}