Ryan Byrd’s Tech Ramblings

reversing a string is a classic tech interview question. of course you’re not allowed to call any built-in reverse() function. A solution might look like, in my pseudocode:

someString = new string("732432424");
char temp;
int end=someString.length()-1;

for (int x=0;x<end;x++)
{
	temp=someString[end];
	someString[x]=someString[end];
	someString[end]=temp;
	end--;
}

but sometimes the interviewer asks you to reverse the string in place, without using other memory, and for that, we’ll need our XOR friend

A B  XOR
----+---
0 0 | 0
0 1 | 1
1 0 | 1
1 1 | 0

someString = new string("732432424");
char temp;
int end=someString.length()-1; //assume zero based char arrays

for (int x=0;x<end;x++)
{
	someString[x]=someString[x] XOR someString[end];
        // first loop: someString[x]=3
	someString[end]=someString[end] XOR someString[x];
        //first loop: someString[end]=7
	someString[x] = someString[x] XOR someString[end];
       //first loop: someString[x]=4
	end--;
}