iframe-proxy | Sunbelt Computer Software

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"""

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.

"""

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()

Sunbelt Computer Software