How Can You Swap Two Variable Values Without Using a Third Variable?

Swapping Variable Values Without a Third Variable: An Interview Puzzle

In software development interviews, a common question is presented: how to swap the values of two variables without using a third variable? Traditionally, this is achieved using a temporary variable as a placeholder.

To bypass the need for a third variable, the xor swap algorithm can be employed. This technique utilizes the exclusive OR operation (XOR), which returns 0 if both bits are the same and 1 if they are different.

XOR Swap Algorithm:

void xorSwap(int* x, int* y) {
    if (x != y) { //ensure that memory locations are different
       *x ^= *y;
       *y ^= *x;
       *x ^= *y;
    }
}

This algorithm works by performing the following steps:

1. Check if x and y refer to different memory locations. If they do, proceed.
2. Perform an XOR operation between *x and *y, storing the result in *x. This essentially flips the bits of *x to match those of *y.
3. Perform another XOR operation between *x and *y, storing the result in *y. This flips the bits of *y to match those of the original *x.
4. Perform a final XOR operation between *x and *y, storing the result in *x. This flips the bits of *x back to their original values.

Considerations:

• It's important to ensure that x and y refer to different memory locations. Otherwise, XORing them will cancel out any changes made.
• This algorithm is generally not used in practice as modern compilers optimize away the need for a temporary variable. However, it showcases the concept of using bitwise operations to achieve complex operations.

The above is the detailed content of How Can You Swap Two Variable Values Without Using a Third Variable?. For more information, please follow other related articles on the PHP Chinese website!