def queens_lex(n: int): def sub(i: int): if i < n: for k in range(i, n): j = a[k] a[i], a[k] = a[k], a[i] if b[i + j] and c[i - j]: b[i + j] = c[i - j] = False yield from sub(i + 1) b[i + j] = c[i - j] = True a[i:(n - 1)], a[n - 1] = a[(i + 1):n], a[i] else: yield a a = list(range(n)) b = [True] * (2 * n - 1) c = [True] * (2 * n - 1) yield from sub(0) next(queens(31)) [0, 2, 4, 1, 3, 8, 10, 12, 14, 6, 17, 21, 26, 28, 25, 27, 24, 30, 7, 5, 29, 15, 13, 11, 9, 18, 22, 19, 23, 16, 20] next(queens_lex(31)) [0, 2, 4, 1, 3, 8, 10, 12, 14, 5, 17, 22, 25, 27, 30, 24, 26, 29, 6, 16, 28, 13, 9, 7, 19, 11, 15, 18, 21, 23, 20] #Compare to A065188 #1, 3, 5, 2, 4, 9, 11, 13, 15, 6, 8, 19, 7, 22, 10, 25, 27, 29, 31, 12, 14, 35, 37, ...