What is the algorithm for swapping two numbers?

Answer 1

In order to swap two values in computer memory you need to temporarily store one of those values during the exchange. That is, to swap the values of object's A and B we must perform the following steps where T is a temporary object:

1. Copy the value of A to T
2. Copy the value of B to A
3. Copy the value of T to B

Note that this algorithm does not implement a "perfect swap". That is, when two people (the objects) swap their house keys (the values), we don't require a third person (the temporary object) to hold a copy of one of those keys, we simply hand the actual keys over (perhaps even simultaneously). No copies are made or indeed required -- we simply "move" values from one place to another.

But a computer cannot move values from one place to another, it has to copy them via assignment. If we assign the value of B to A then both A and B would hold the same value. The original value of A is lost, hence we require a temporary object to hold the value of A.

Note that although languages like C++ support a native move operation, the move operation applies to resource handles only. When we swap a resource, the resources don't actually move, the only thing that changes is the "owner" of the resource. That is, it is the handle's that swap, not the resources. Even so, with move semantics we still need a temporary:

1. Move ownership of A's resource to T
2. Move ownership of B's resource to A
3. Move ownership of T's resource to B

This is as close to the "perfect swap" as we can get, but it does not apply to primitive data types like numbers because the notion of "ownership" only applies to resource handles. The most efficient way to "move" a primitive data type is simply to copy it.

Answer 2

When we perform a swap we exchange the values of two and only two variables at a time. So to swap three values, A, B and C, we would first need to swap A with B, and then swap C with either A or B. Given that there are two possible outcomes, there is no single algorithm that can perform a three-way swap.

Answer 3

Using a temporary variable

temp = a

a = b

b = temp

Without a temporary variable

a = a+b

b=a-b

a = a-b

Answer 4

Step 1: Start

step 2: read 'a' and 'b' value

step 3: inter change the values

temp=a

a=b

b=temp

step 4: write a and b values.

step 5:stop

Answer 5

The algorithm to swap two numbers identified as a and b is as follows:

temp = a

a = b

b = temp

Answer 6

To swap two variables of type T named a and b, use the following algorithm:

T temp = a;

a = b;

b = temp;

Answer 7

void swap (int* a, int* b) {(*a) ^= (*b) ^= (*a) ^= (*b);

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