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* pre-commit: Upgrade psf/black for stable style 2023 Updating https://github.com/psf/black ... updating 22.12.0 -> 23.1.0 for their `2023 stable style`. * https://github.com/psf/black/blob/main/CHANGES.md#2310 > This is the first [psf/black] release of 2023, and following our stability policy, it comes with a number of improvements to our stable style… Also, add https://github.com/tox-dev/pyproject-fmt and https://github.com/abravalheri/validate-pyproject to pre-commit. I only modified `.pre-commit-config.yaml` and all other files were modified by pre-commit.ci and psf/black. * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci --------- Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
46 lines
1.3 KiB
Python
46 lines
1.3 KiB
Python
"""
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The nested brackets problem is a problem that determines if a sequence of
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brackets are properly nested. A sequence of brackets s is considered properly nested
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if any of the following conditions are true:
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- s is empty
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- s has the form (U) or [U] or {U} where U is a properly nested string
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- s has the form VW where V and W are properly nested strings
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For example, the string "()()[()]" is properly nested but "[(()]" is not.
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The function called is_balanced takes as input a string S which is a sequence of
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brackets and returns true if S is nested and false otherwise.
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"""
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def is_balanced(s):
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stack = []
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open_brackets = set({"(", "[", "{"})
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closed_brackets = set({")", "]", "}"})
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open_to_closed = dict({"{": "}", "[": "]", "(": ")"})
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for i in range(len(s)):
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if s[i] in open_brackets:
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stack.append(s[i])
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elif s[i] in closed_brackets:
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if len(stack) == 0 or (
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len(stack) > 0 and open_to_closed[stack.pop()] != s[i]
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):
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return False
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return len(stack) == 0
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def main():
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s = input("Enter sequence of brackets: ")
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if is_balanced(s):
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print(s, "is balanced")
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else:
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print(s, "is not balanced")
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if __name__ == "__main__":
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main()
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