12 Reverse String using XOR and without using Temporary Variable

By Surendar N

12

Reverse String using XOR and without using Temporary Variable

Posted in

My friend faced this question for TCS technical interview. The code the much simple but the logic is bit complex

char* rev(char* str)

{
int end= strlen(str)-1;
int start = 0;

while( start<end )
{
str[start] ^= str[end];
str[end] ^= str[start];
str[start]^= str[end];

++start;
--end;
}

return str;
}

The the above version is with while loop even one can use for loop instead of it.

XOR (Exclusive OR) table

0 XOR 0 = 0

0 XOR 1 = 1

1 XOR 0 = 1

1 XOR 1 = 0

So how does it works.

First operation:	x1 = x1 XOR x2
x1:	1	0	0
x2:	1	1	1
New x1:	0	1	1
Second operation	x2 = x2 XOR x1
x1:	0	1	1
x2:	1	1	1
New x2:	1	0	0
Third operation:	x1 = x1 XOR x2
x1:	0	1	1
x2:	1	0	0
New x1:	1	1	1

So finally we have done X1 and X2 are swapped. This method is for both without using Temporary variable and also using Xor operator...

Pretty Cool huh...