C 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 

👁 check-for-balanced-parentheses-in-an-expression

Algorithm: 

• Declare a character stack S.
• Now traverse the expression string exp. 
  
  1. If the current character is a starting bracket ('(' or '{' or '[') then push it to stack.
  2. 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:

👁 Image

Below is the implementation of the above approach:

Balanced

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!