bracket-push: Add test case "partially paired brackets"

[mrcfps]

Some incorrect solutions return true as soon as brackets are matched. Check out this solution in Python which can pass all current tests:

bracket_dict = {"(": ")", "[": "]", "{": "}"}


def brackets_match(opening_bracket, closing_bracket):
    return bracket_dict[opening_bracket] == closing_bracket


def is_paired(input_string):
    bracket_stack = []
    # Add every "opening" bracket to the stack
    # if we encounter a "closing" bracket, it should match the current
    # bracket on top of the stack
    for char in input_string:
        # If we encounter an opening bracket, we add it on top of the stack
        if char in bracket_dict.keys():
            bracket_stack.append(char)
        elif char in bracket_dict.values():
            # Get the bracket on top of the stack
            try:
                top_of_stack = bracket_stack.pop()
            # If the bracket_stack is empty, then we return false, since
            # the closing bracket has no opening bracket pair
            except IndexError:
                return False

            # Check and return if the opening and closing brackets match
            return brackets_match(top_of_stack, char)

    # Once done processing the string, bracket_stack should be empty
    # If empty, this means that all brackets have been matched
    # If not empty, this means that some brackets remain unmatched
    return bracket_stack == []

Clearly return brackets_match(top_of_stack, char) within the for loop is wrong, so it will fail test cases where brackets are partially paired, like {[]).

[petertseng]

I confirm that such a described implementation (early return) passes all tests but not the new one.

Please designate that in the commit message. The PR description was good because it explains why the test case is added; the information should be in the commit message as well so that the information is visible without having to visit GitHub.

Commits should be squashed.

If nothing else, around 24 hours from now I will make both things happen.

[mrcfps]

@petertseng Done at your request.

[petertseng]

cool. I could quibble a bit about "once brackets are matched" -> "once any one pair of brackets is matched" to really distinguish it from solutions that check all pairs of brackets as they should, but I haven't the time to write down all my thoughts, and it's good as-is anyway.