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Description

Swap two integers without using a 3rd variable!

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Submitted On
By	Junaidulla
Level	Intermediate
User Rating	4.5 (27 globes from 6 users)
Compatibility	Java (JDK 1.1), Java (JDK 1.2)
Category	Miscellaneous
World	Java
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Source Code

Swap Two ints Without Using a Third Variable
Here's an old trick from C, which carries over to
Java. If you have two ints a and b whose
values you want to swap, the obvious way to
do so is with a third, temporary variable:
int c = a;
a = b;
b = c;
It can be done without a temporary variable,
however, using Java's bitwise xor operator ^:
a = a^b;
b = a^b;
a = a^b;
The operator ^ produces a new int, each of whose
bits is the result of xor-ing the two
corresponding bits from the operands (1 if
the bits are different, 0 otherwise). To see why the trick works, consider the single-bit case
of a=1 and b=0.
a = a^b = 1 xor 0 = 1
b = a^b = 1 xor 0 = 1
a = a^b = 1 xor 1 = 0
Even though you initially overwrite the value of
a, no information is lost; its encoding
simply changes. In the case of larger (multi-bit)
numbers, each pair of bits will be swapped
in the same way, and so the entire int values are swapped.
Finally, the swapping code can be made even more
succinct:
a ^= b ^= a ^= b;