data-structures Stack Checking Balanced Parentheses
Example
A bracket is considered to be any one of the following characters: (, ), {, }, [, or ].
Two brackets are considered to be a matched pair if the an opening bracket (i.e., (, [, or {) occurs to the left of a closing bracket (i.e., ), ], or }) of the exact same type. There are three types of matched pairs of brackets: [], {}, and ().
A matching pair of brackets is not balanced if the set of brackets it encloses are not matched. For example, {[(])} is not balanced because the contents in between { and } are not balanced. The pair of square brackets encloses a single, unbalanced opening bracket, (, and the pair of parentheses encloses a single, unbalanced closing square bracket, ].
By this logic, we say a sequence of brackets is considered to be balanced if the following conditions are met:
It contains no unmatched brackets.
The subset of brackets enclosed within the confines of a matched pair of brackets is also a matched pair of brackets.
Algorithm:
- Declare a stack (say
stack). - Now traverse the string input.
- a) If the current character is a starting bracket ( i.e.
(or{or[) then push it to stack. - b) If the current character is a closing bracket ( i.e.
)or}or]) then pop from stack. If the popped character is the matching starting bracket then fine else parenthesis arenot balanced. - c) If the current character is a closing bracket ( i.e.
)or}or]) and the stack is empty, then parenthesis arenot balanced.
- After complete traversal, if there is some starting bracket left in stack then the string is
not balancedelse we have abalancedstring.
