mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-12-18 17:20:16 +00:00
51 lines
1.3 KiB
Python
51 lines
1.3 KiB
Python
'''
|
|
The nested brackets problem is a problem that determines if a sequence of
|
|
brackets are properly nested. A sequence of brackets s is considered properly nested
|
|
if any of the following conditions are true:
|
|
|
|
- s is empty
|
|
- s has the form (U) or [U] or {U} where U is a properly nested string
|
|
- s has the form VW where V and W are properly nested strings
|
|
|
|
For example, the string "()()[()]" is properly nested but "[(()]" is not.
|
|
|
|
The function called is_balanced takes as input a string S which is a sequence of brackets and
|
|
returns true if S is nested and false otherwise.
|
|
|
|
'''
|
|
from __future__ import print_function
|
|
|
|
|
|
def is_balanced(S):
|
|
|
|
stack = []
|
|
open_brackets = set({'(', '[', '{'})
|
|
closed_brackets = set({')', ']', '}'})
|
|
open_to_closed = dict({'{':'}', '[':']', '(':')'})
|
|
|
|
for i in range(len(S)):
|
|
|
|
if S[i] in open_brackets:
|
|
stack.append(S[i])
|
|
|
|
elif S[i] in closed_brackets:
|
|
if len(stack) == 0 or (len(stack) > 0 and open_to_closed[stack.pop()] != S[i]):
|
|
return False
|
|
|
|
return len(stack) == 0
|
|
|
|
|
|
def main():
|
|
|
|
S = input("Enter sequence of brackets: ")
|
|
|
|
if is_balanced(S):
|
|
print((S, "is balanced"))
|
|
|
|
else:
|
|
print((S, "is not balanced"))
|
|
|
|
|
|
if __name__ == "__main__":
|
|
main()
|