Python Program To Check For Balanced Brackets In An Expression (Well-Formedness) Using Stack
Given an expression string exp, write a program to examine whether the pairs and the orders of “{“, “}”, “(“, “)”, “[“, “]” are correct in exp.
Example:
Input: exp = “[()]{}{[()()]()}”
Output: Balanced
Input: exp = “[(])”
Output: Not Balanced
Algorithm:
- Declare a character stack S.
- Now traverse the expression string exp.
- If the current character is a starting bracket (‘(‘ or ‘{‘ or ‘[‘) then push it to stack.
- If the current character is a closing bracket (‘)’ or ‘}’ or ‘]’) then pop from stack and if the popped character is the matching starting bracket then fine else brackets are not balanced.
- After complete traversal, if there is some starting bracket left in stack then “not balanced”
Below image is a dry run of the above approach:
Below is the implementation of the above approach:
Python3
def areBracketsBalanced(expr):
stack = []
for char in expr:
if char in [ "(" , "{" , "[" ]:
stack.append(char)
else :
if not stack:
return False
current_char = stack.pop()
if current_char = = '(' :
if char ! = ")" :
return False
if current_char = = '{' :
if char ! = "}" :
return False
if current_char = = '[' :
if char ! = "]" :
return False
if stack:
return False
return True
if __name__ = = "__main__" :
expr = "{()}[]"
if areBracketsBalanced(expr):
print ( "Balanced" )
else :
print ( "Not Balanced" )
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Time Complexity: O(n)
Auxiliary Space: O(n) for stack.
Please refer complete article on Check for Balanced Brackets in an expression (well-formedness) using Stack for more details!
Last Updated :
19 May, 2022
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