'''
Implement an algorithm to print all valid (e.g. properly opened and closed) combinations of n pairs of parentheses.

Example:
    Input: 3
    Output: ((())), (()()), (())(), ()(()), ()()()

Hints: 138, 174, 187, 209, 243, 265, 295
'''


def parens(s):
    pass

if __name__ == '__main__':
    assert parens('') ==
    assert parens('') ==
    assert parens('') ==
    assert parens('') ==
    assert parens('') ==
