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

Given a string s containing just the characters (, ), {, }, [ and ], determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order.

/**
* @param {string} s
* @return {boolean}
*/
// O(N) time, O(N) space
var isValid = function(s) {
 if (s.length === 0) {
   return true;
 }
 
 const brackets = {
   "{": "}",
   "(": ")",
   "[": "]",
 };
 
 
 const stack = [];
 
 for (let bracket of s) {
   const isOpenBracket = brackets.hasOwnProperty(bracket);
   // Push open brackets onto the stack
   if (isOpenBracket) {
     stack.push(bracket);
   } else {
   // For closed brackets we make sure we can find the matching open bracket at the top of the stack
     if (stack.length === 0) {
       return false;
     }


     const currentOpenBracket = stack[stack.length - 1];
     if (brackets[currentOpenBracket] !== bracket) {
       return false;
     }


     // If they matched, we remove the top open bracket
     stack.pop();
   }
 }
 
 // Assuming all the brackets are matched and accounted for, we return true
 return stack.length === 0;
};