Any programming language may be used. 3 points will be given if you pass all the test cases with 1 bonus point going to whoevers performs the quickest and 1 for whoever can get the least amount of characters
To submit put the code and the language you used below
I actually found this challenge to be easier than this week's medium challenge. (Watch me say that and get this wrong while also getting the medium one correct...) Here's an O(n) solution:
bracket_pairs = {('(', ')'), ('[', ']'), ('{', '}')}
def main(brackets: str) -> str:
n = len(brackets)
has_match_at = {i: False for i in range(-1, n + 1)}
acc = []
for i, bracket in enumerate(brackets):
acc.append((i, bracket))
if len(acc) >= 2:
opening_idx, opening = acc[-2]
closing_idx, closing = acc[-1]
if (opening, closing) in bracket_pairs:
acc.pop(), acc.pop()
has_match_at[opening_idx] = has_match_at[closing_idx] = True
longest_start, longest_end = 0, 0
most_recent_start = None
for left_idx, right_idx in zip(range(-1, n), range(0, n + 1)):
has_match_left = has_match_at[left_idx]
has_match_right = has_match_at[right_idx]
if (has_match_left, has_match_right) == (False, True):
most_recent_start = right_idx
if (has_match_left, has_match_right) == (True, False):
most_recent_end = right_idx
if most_recent_end - most_recent_start > longest_end - longest_start:
longest_start, longest_end = most_recent_start, most_recent_end
return brackets[longest_start:longest_end]
if __name__ == '__main__':
from argparse import ArgumentParser
parser = ArgumentParser()
parser.add_argument('brackets')
print(main(parser.parse_args().brackets))
We start off by doing the same thing as this week's easy challenge, except we keep track of the indices of all of the matched brackets that we remove (opening or closing). We then identify the longest stretch of consecutive removed-bracket indices, and use that information to slice into the input to get the output.
For ease of implementation of the second part, I modelled the removed-bracket indices with a dict simulating a list indexed by [-1 .. n + 1), with the values indicating whether the index corresponds to a matched bracket. The extra elements on both ends are always set to False. For example, {([])()[(])}()] -> FFTTTTTTFFFFFTTFF, and ([{}]) -> FTTTTTTF. To identify stretches of consecutive indices, we can simply watch for when the value switches from False to True (start of a stretch), and from True to False (end of a stretch). We do that by pairwise-looping through the dict-list, looking for 'FT' and 'TF'.