Swap two numbers with and without a third variable

Description: Swap the values of a = 10 and b = 25. First use a third variable. Then do it without a third variable.

Hint:

• With three variables: temp = a; a = b; b = temp;
• Without: use addition and subtraction.

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Solution

public class Main {
    public static void main(String[] args) {
        int a = 10, b = 25;

        int temp = a;           // way 1: a third variable
        a = b;
        b = temp;
        System.out.println("a = " + a + ", b = " + b);

        a = a + b;              // way 2: no third variable
        b = a - b;
        a = a - b;
        System.out.println("a = " + a + ", b = " + b);
    }
}

How it works

• The first way keeps one value safe in temp before it is replaced.
• In the second way, a becomes the sum, and then each variable gets the other value by subtraction. (Be careful: with very big numbers the sum can overflow.)

Read Java Operators.

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