Greetings! Today, we're drawing back the curtains on Stacks in JavaScript, a crucial data structure. A stack
is like a pile of dishes: you add a dish to the top (Last In) and take it from the top (First Out). This Last-In, First-Out (LIFO) principle exemplifies the stack. JavaScript executes stacks effortlessly using Arrays
. This lesson will illuminate the stack data structure, operations, and their JavaScript applications. Are you ready to start?
A stack
is an elongated storehouse permitting Push
(addition) and Pop
(removal) operations. It's akin to a stack of plates in a cafeteria where plates are added (pushed
) and removed (popped
) from the top. No plate can be taken from the middle or the bottom, exemplifying a Last-In, First-Out (LIFO) operation.
To create a stack, JavaScript employs a built-in data structure known as an Array
. For the Push
operation, we use push()
, which adds an element at the array's end. For the Pop
operation, there's the pop()
function that removes the last element, simulating the removal of the 'top' element in a stack. Here's how it looks:
In the example provided, we push 'John'
, 'Mary'
, and 'Steve'
into the stack and then pop 'Steve'
from the stack.
Stacks' operations go beyond merely push
and pop
. For example, to verify if a stack is empty, we can use the length
property. If it returns 0, that means the stack is empty. Conversely, if it returns a nonzero value, we can infer the stack is not empty. To peek at the top element of the stack without popping it, merely indexing with stack[stack.length - 1]
is handy.
Here's an example:
In this example, 'Sam'
is added (pushed
), and then the topmost stack element, which is 'Sam'
, is peeked at.
Practical applications of stacks in JavaScript are plentiful. Here is one of them — reversing a string.
We will push all characters into a stack and then pop them out to get a reversed string!
A stack can be utilized to verify if parentheses in an expression are well-matched, i.e., every bracket has a corresponding pair. For example, parentheses in the string "()[{}]"
are well-matched, while in the strings "([]()"
, ")()[]{}"
, "([)]"
, and "[{})"
they are not.
Let's break down the solution into simple steps:
We start by creating an object that maps each closing bracket to its corresponding opening bracket and an empty stack. Then, we iterate over each character paren
in the string parenString
:
- If
paren
is an opening bracket, it gets appended to the stack. - If
paren
is a closing bracket and the top element in the stack is the corresponding opening bracket, we remove the top element from the stack. - If neither of the above conditions is met, we return
false
.
Finally, if the stack is empty (all opening brackets had matching closing brackets), we return true
. If there are some unmatched opening brackets left, we return false
.
Kudos to you! Having covered the stack data structure, operations, and their JavaScript applications is a commendable feat. Next up, you'll encounter practice exercises that will solidify your newly acquired knowledge. Dive into them and master Stacks in JavaScript!
