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SumOfDigits.java

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package Maths;

public class SumOfDigits {

public static void main(String[] args) {

assert

sumOfDigits(-123) == 6

&& sumOfDigitsRecursion(-123) == 6

&& sumOfDigitsFast(-123) == 6;

assert sumOfDigits(0) == 0

&& sumOfDigitsRecursion(0) == 0

&& sumOfDigitsFast(0) == 0;

assert sumOfDigits(12345) == 15

&& sumOfDigitsRecursion(12345) == 15

&& sumOfDigitsFast(12345) == 15;

}

/**

* Calculate the sum of digits of a number

*

* @param number the number contains digits

* @return sum of digits of given {@code number}

*/

public static int sumOfDigits(int number) {

number = number < 0 ? -number : number; /* calculate abs value */

int sum = 0;

while (number != 0) {

sum += number % 10;

number /= 10;

}

return sum;

}

/**

* Calculate the sum of digits of a number using recursion

*

* @param number the number contains digits

* @return sum of digits of given {@code number}

*/

public static int sumOfDigitsRecursion(int number) {

number = number < 0 ? -number : number; /* calculate abs value */

return number < 10 ? number : number % 10 + sumOfDigitsRecursion(number / 10);

}

/**

* Calculate the sum of digits of a number using char array

*

* @param number the number contains digits

* @return sum of digits of given {@code number}

*/

public static int sumOfDigitsFast(int number) {

number = number < 0 ? -number : number; /* calculate abs value */

char[] digits = (number + "").toCharArray();

int sum = 0;

for (int i = 0; i < digits.length; ++i) {

sum += digits[i] - '0';

}

return sum;

}

}