eight queens puzzle.c

#include "stdio.h"
 
#define SIZE 8
 
void printrow(unsigned int q)
{
	for (int i=0; i < SIZE; i++)
	{
		char c = (q >> i) & 1 ? '*' : '.';
		putchar(c);
	}
	putchar('n');
}
 
extern void placeQ(int x, int y)
{
	static unsigned int Q[SIZE];
	static unsigned int nSolutions;
 
	unsigned int col0, col1, col2,q;
	col0 = 1 << (SIZE - 1 - x);
	for (int row = 0; row < y; row++)
	{
		col1 = col0 << (y - row);
		col2 = col0 >> (y - row);
		q = Q[row];
		if (q == col0 || q == col1 || q == col2) goto nextcolumn;
	}
 
	Q[y] = col0;
	if (y == SIZE - 1) // finished
	{
		printf("nSolution #%d:n", ++nSolutions);
		for (int i = 0; i < SIZE; i++) printrow(Q[i]);
	}
	else
	{
		// continue to try next row
		placeQ(0, y + 1);
	}
	Q[y] = 0;
 
nextcolumn:	
	if (x < SIZE - 1) placeQ(x + 1, y);
}
 
int main (int argc, char const *argv[])
{
	placeQ(0, 0);
	return 0;
}