Thread: permutation

I didn't have a clue where to start on this help-free challenge. So I examined the solution and then stared blankly at it.
Please explain this:

Code:

#include <iostream>
#include <string>

string switch(string topermute, int x, int y)
{
	string newstring = topermute;
	newstring[x] = newstring[y];
	newstring[y] = topermute[x]; //avoids temp variable
	return newstring;
}
void permute(string topermute, int place)
{
	if(place == topermute.length - 1)
	{
		cout<<topermute<<endl;
	}
	for(int nextchar = place; nextchar < 
	    topermute.length(); nextchar++)
	{
		permute(switch(topermute, place, nextchar),
		        place+1);
	}
}

int main(int argc, char* argv[])
{
	if(argc!=2)
	{
		cout<<"Proper input is 'permute string'";
	}
	else
	{
		permute(argv[1], 0);
	}
	return 0;
}

Sure. Would you like some beer while we explain it to you?

Oh well then tell the webmaster that cause I copy and pasted into the post.