“Valid Parentheses” Cheat Sheet javascript solution

The Valid Parentheses is in the easy category and is a good start for understanding more challenging algorithms using the stack and array as a data structure. I will focus on explaining a solution that works and not on the O time and space complexity.

Challenge:

“Given a string s containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[‘ and ‘]’, determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.”LeetCode

Note:

// String s
// Determine if valid
// Valid = same type brackets && open/closed in correct order
// Empty string = true
// Return boolean 

Example:

Input: s = “[]”
Output: true

Explanation:

create a valid brackets object to compare to a stack that will store the string brackets and return true or false.

1.Create an object of valid brackets

let validBracket = {
‘(‘:’)’,
‘{‘:’}’,
‘[‘:’]’
}

2. Create an array to sort the stack

let stack =[];

3. Loop through the string s

for (let char of s ) {

4. Check if validBracket

if (validBracket[char]){

5. If valid push through the stack

stack.push(validBracket[char])

6. If the last character not equal to char it is false

if (stack.pop()!== char ) return false

Solution:

var isValid = function(s) {
let validBracket = {
‘(‘:’)’,
‘{‘:’}’,
‘[‘:’]’
}
let stack =[];
for (let char of s ) {
if (validBracket[char]){
stack.push(validBracket[char])
} else {
if (stack.pop()!== char ) return false
}
}
return (!stack.length)
};