Brackets

Input: An expression with different of types brackets as a string (unicode).

Output: A verdict on the correctness of the expression in boolean (True or False).

Example:

checkio("((5+3)*2+1)") == True

checkio("{[(3+1)+2]+}") == True

checkio("(3+{1-1)}") == False

checkio("[1+1]+(2*2)-{3/3}") == True

checkio("(({[(((1)-2)+3)-3]/3}-3)") == False

checkio("2+3") == True

How it is used: When you write code or complex expressions in a mathematical package, you can get a huge headache when it comes to excess or missing brackets. This concept can be useful for your own IDE.

Precondition:
There are only brackets ("{}" "()" or "[]"), digits or operators ("+" "-" "*" "/").
0 < len(expression) < 103

def checkio(expression):
    OPEN = ('(', '{', '[')
    CLOSE = (')', '}', ']')
    
    stack = []
    for alpha in expression:
        if alpha in OPEN:
            stack.append(alpha)
        elif alpha in CLOSE:
            if len(stack) == 0:
                return False
            else:
                last = stack.pop()
                if OPEN.index(last) != CLOSE.index(alpha):
                    return False
    
    if len(stack) != 0:
        return False
    
    return True
    

#These "asserts" using only for self-checking and not necessary for auto-testing
if __name__ == '__main__':
    assert checkio("((5+3)*2+1)") == True, "Simple"
    assert checkio("{[(3+1)+2]+}") == True, "Different types"
    assert checkio("(3+{1-1)}") == False, ") is alone inside {}"
    assert checkio("[1+1]+(2*2)-{3/3}") == True, "Different operators"
    assert checkio("(({[(((1)-2)+3)-3]/3}-3)") == False, "One is redundant"
    assert checkio("2+3") == True, "No brackets, no problem"

これは前にRubyで似たようなのを解いた記憶がある。スタックにどんどん入れていって、調べれば良い。

pythonで定数を扱うなら、リストよりもタプルのほうが高速。
また、指定の値を持つかどうかを調べるときはindex関数を使えばOK.