Solving Coding Challenges: Validating Brackets with TypeScript

Leetcode Problem Question

https://leetcode.com/problems/valid-parentheses/

Updated On: Sept 15, 2023

Main things to note

Object We're using Object to save the opening and closing of the parentheses
Stack As you know stack works in a LIFO (Last In First Out) manner. So, you can get the last parenthesis you added and then match it with the object value.

stack parenthesis.png

Javascript Solution

/**
 * @param {string} s
 * @return {boolean}
 */
var isValid = function(s) {
     let parenthesesMap = { ')': '(', '}': '{', ']': '[' };

  let stack = new Stack();

  //With Mapping
  for (let index = 0; index < s.length; index++) {
    const element = stack.getPopItem();

    if (Object.values(parenthesesMap).includes(s[index])) {
      stack.push(s[index]);
    }
    else if ((element === parenthesesMap[s[index]])) {
      stack.pop();
    } else return false;
  }

  // if Stack has value that means some open parenthesis are there
  return (stack.isEmpty()) ? true : false;
};


const s = "()[{]"
console.log(isValid(s));

class Stack {

    constructor() {
        this.items = [];
    }

    peek(){
        this.items.shift();
    }

    push(element){
        this.items.push(element);
    }

    //Get the last digit
    pop(){
        // console.log(this.items);
        return this.items.pop();
    }

    isEmpty(){
        return (this.items.length === 0)? true:false;
    }

    printStack(){
        console.log(this.items);
    }

    getSize(){
        return this.items.length;
    }

    getPopItem(){
        return this.items[this.items.length -1];
    }
}

Leetcode Result

Another Solution

If you're looking for an alternate coding solution. Please check the below. I am also adding the description I got from ChatGPT (this looks good to read :) )

function isValid(s: string): boolean {
    if(s.length ==1) return false;

    const brackets = {
        '(':')',
        '[':']',
        '{':'}',
    }

    const vals = s.split("");
    let stackArr = [];


    for (const val of vals){

        //If stackArr val is ( )
        let stackArrLength = stackArr.length-1;
        if(val != brackets[stackArr[stackArrLength]]) {
            stackArr.push(val);
            continue;
        }

        stackArr.splice(-1); //remove last item from array;

    }

    if(stackArr.length >0) return false;

    return true;
};

Here's a step-by-step description of the code:

Input Validation:

The function begins by checking if the input string s has a length of 1. If it does, it immediately returns false. This check ensures that single characters cannot be considered valid bracket expressions.

Brackets Mapping:

The code defines an object named brackets to map the opening brackets to their corresponding closing brackets. This mapping includes ( to ), [ to ], and { to }. This mapping is crucial for later bracket matching.

String Splitting:

The input string s is split into an array of characters named vals. This array will be iterated over to process each character in the input string.

Stack Initialization:

An empty array named stackArr is created. This array will be used as a stack to keep track of the opening brackets encountered in the input string.

Bracket Matching Loop:

The code enters a loop that iterates through each character (val) in the vals array.

In summary, the code utilizes a stack data structure to keep track of opening brackets and checks if the input string contains a valid bracket expression by ensuring that all opening brackets are correctly closed in the right order. If the brackets are properly balanced and nested, the function returns true; otherwise, it returns false.

Valid Parentheses Using Javascript - LeetCode Challenges

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Leetcode Problem Question

Main things to note

Javascript Solution

Leetcode Result

Another Solution

Command Palette

Comments

Coding Challenges

Compress String using Javascript

More from this blog

Leetcode Problem Question

Main things to note

Javascript Solution

Leetcode Result

Another Solution