Permutations in C++

permut.cpp

/*
 * Print all permutations of string ``s´´. (C++)
 *
 * Solved as a counting problem and coded in a hurry.
 * 
 * A more elegant and recursive solution:
 * http://nicolas-lara.blogspot.com/2009/01/permutations.html
 */

#include <stdio.h>

static const char s[] = "abc";
const int MAX = (sizeof(s)/sizeof(char)) - 1;

void print(int counts[MAX])
{
	for ( int n=0; n<MAX; ++n )
		printf("%c", s[counts[n]]);
	printf("\n");
}

void inc(int counts[MAX], int p = 0)
{
	if ( p < MAX && ++counts[p] >= MAX ) {
		counts[p] = 0;
		inc(counts, p+1);
	}
}

bool zero(int counts[MAX])
{
	for ( int p=0; p < MAX; ++p )
		if ( counts[p] != 0 )
			return false;
	return true;
}

/*
 * Are all indices unique?
 */
bool uniq(int counts[MAX])
{
        int x = 0;
	for ( int n=0; n<MAX; ++n )
		x ^= counts[n] ^ n;
	return x == 0;
}

int main()
{
	int counts[MAX] = {0};

	do {
		if ( uniq(counts) )
			print(counts);
		inc(counts);
	} while ( !zero(counts) );
}

Made uniq run in O(n) instead of O(n^2).