Data commit

Task/Weird-numbers/Java/weird-numbers.java

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+import java.util.ArrayList;
+import java.util.List;
+
+public class WeirdNumbers {
+
+    public static void main(String[] args) {
+        int n = 2;
+        //  n += 2 : No odd weird numbers < 10^21
+        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;
+    }
+
+    //  Use Dynamic Programming
+    private static boolean isSemiPerfect(List<Integer> divisors, int sum) {
+        int size = divisors.size();
+
+        //  The value of subset[i][j] will be true if there is a subset of divisors[0..j-1] with sum equal to i
+        boolean subset[][] = new boolean[sum+1][size+1];
+
+        // If sum is 0, then answer is true
+        for (int i = 0; i <= size; i++) {
+            subset[0][i] = true;
+        }
+
+        //  If sum is not 0 and set is empty, then answer is false
+        for (int i = 1; i <= sum; i++) {
+            subset[i][0] = false;
+        }
+
+        // Fill the subset table in bottom up manner
+        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;
+    }
+
+}