Balanced Brackets

Balanced Brackets | Stacks

In this post we will explore and implement an algorithm which helps us verify that if the brackets are balanced or validly used. This is a very important application of stacks as a lot of programming languages use brackets very extensively in their syntax and one of the job of a compiler is to check if the brackets are balanced or not. For simplicity's sake we will just use a list with the methods append() and pop(). This will help us emulate a stack without actually needing to implement it. If you want to, you can go and learn about stacks on this link.

A set of brackets can be called balanced if all of the brackets in it are properly matched.
Examples of balanced brackets :

(([]{}{}))
({{}}[])

Examples of unbalanced brackets :
(([)])
{{}]}]])

So now getting to the algorithm, what we simply do is that we go through a string of brackets and check that for every closing bracket there is a properly nested opening bracket.
This is how we do it -

Convert the input string into a list.
Traverse the list
1. If we see an opening bracket, push it to the stack.
2. When we encounter a closing bracket, check if it is equal to the opening bracket that we pop from the stack.
If the stack is empty, return true. If not, return false.

Here's how we will implement it -

This algorithm can very easily be coupled with the other application of stacks, Expression Evaluation. Bracket Balancing can be used with it to validate the expressions entered by the user. To learn about Expression Evaluation using Stacks follow this link

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