Java Number Sum sumOfProperDivisors(long num)

Description

sum Of Proper Divisors

License

Apache License

Declaration

public static long sumOfProperDivisors(long num) 

Method Source Code

//package com.java2s;
/**/*from   ww  w  . j av a 2  s  .  c om*/
 *
 * maer - Solutions to problems of Project Euler
 * Copyright (C) 2011, Sandeep Gupta
 * http://www.sangupta.com/projects/maer
 *
 * The file is licensed under the the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

public class Main {
    public static long sumOfProperDivisors(long num) {
        if (num == 1) {
            return 0;
        }

        long sum = 1; // as 1 is a divisor and we are considering proper divisors
        long root = (long) Math.sqrt((double) num);

        if (root * root == num) {
            // case that n is a perfect square
            sum += root;
            root -= 1;
        }

        if (isOdd(num)) {
            for (int i = 2; i <= root; i += 2) {
                if (num % i == 0)
                    sum += i + num / i;
            }
        } else {
            // number is even
            for (int i = 2; i <= root; i += 1) {
                if (num % i == 0)
                    sum += i + num / i;
            }
        }

        return sum;
    }

    /**
     * Tests whether the given number is odd or not, uses bit arithmetic.
     * 
     * @param number
     * @return
     */
    public static boolean isOdd(long number) {
        return (number & 1) == 1;
    }
}

Related

1. summatory(int value)
2. sumMinMax(int a, int b)
3. sumNforOddIndices(long n)
4. sumOfCollectionDouble(Iterable doubleIterable)
5. sumOfDigits(long n)
6. sumOr0(Object a, Object b)
7. sumOverOne(final int n)
8. sumPossitiveIntegerSequencePartial(int start, int end)
9. sumUp(final Iterable values)