คุณสมบัติของโปรแกรม · การวางควีนแบบจำกัด

def queens(size):
    if type(size) is not int or not 0 <= size <= 8:
        raise ValueError("size.range")
    result = []
    def visit(columns, down, up):
        row = len(columns)
        if row == size:
            result.append(tuple(columns))
            return
        for column in range(size):
            if column not in columns and row-column not in down and row+column not in up:
                visit(columns + [column], down | {row-column}, up | {row+column})
    visit([], set(), set())
    return result