Python/data_structures/stacks/balanced_parentheses.py

39 lines
1.1 KiB
Python
Raw Normal View History

from .stack import Stack
2018-10-19 12:48:28 +00:00
def balanced_parentheses(parentheses: str) -> bool:
"""Use a stack to check if a string of parentheses is balanced.
>>> balanced_parentheses("([]{})")
True
>>> balanced_parentheses("[()]{}{[()()]()}")
True
>>> balanced_parentheses("[(])")
False
>>> balanced_parentheses("1+2*3-4")
True
>>> balanced_parentheses("")
True
"""
stack: Stack[str] = Stack()
bracket_pairs = {"(": ")", "[": "]", "{": "}"}
for bracket in parentheses:
if bracket in bracket_pairs:
stack.push(bracket)
elif bracket in (")", "]", "}") and (
stack.is_empty() or bracket_pairs[stack.pop()] != bracket
):
return False
return stack.is_empty()
2018-10-19 12:48:28 +00:00
2019-10-05 05:14:13 +00:00
if __name__ == "__main__":
from doctest import testmod
testmod()
2019-10-05 05:14:13 +00:00
examples = ["((()))", "((())", "(()))"]
print("Balanced parentheses demonstration:\n")
2018-10-19 12:48:28 +00:00
for example in examples:
not_str = "" if balanced_parentheses(example) else "not "
print(f"{example} is {not_str}balanced")