Solve the 'balanced delimiters' problem

balanced-delimiters.js

#!/usr/bin/env node
'use strict';

var Delimiters = {
    '[': ']'
  , '(': ')'
  , '{': '}'
}

// Javascript doesn't contain Sets, so we just use a map with booleans.
var Closers = {
    ']': true
  , ')': true
  , '}': true
}

// Checks that the string contains only matching delimiters.
// Delimiters are '(', '[' or '{' and their respective closing characters.
// See https://www.hackerrank.com/contests/programming-interview-questions/challenges/balanced-delimiters
//
// This algorithm time complexity is linear, that is, O(n). Space complexity is
// also linear in the worst case (eg. '[[[[[]]]]]'). A possible space
// improvement is to store a counter for consecutive similar delimiters in the
// stack, but it does not improve the worst case complexity
// (eg. '({[({[]})]})').
//
function checkDelimiters(str) {
    // We'll store all the expected closing characters in a stack.
    var stack = []

    // Let's just go through the whole string.
    for (var i = 0; i < str.length; ++i) {

        // A closing character?
        if (Closers.hasOwnProperty(str[i])) {

            // If the stack is non-empty, and the character matches what we
            // expect next (top of the stack), discard it and continue.
            if (stack.length > 0 && str[i] === stack[stack.length - 1]) {
                stack.pop()
                continue
            }

            // Otherwise, that's a failure.
            return false
        }

        // Ignore non-delimiter characters.
        if (!Delimiters.hasOwnProperty(str[i]))
            continue;

        // Just push the expected closing character on our stack.
        stack.push(Delimiters[str[i]])

    }

    // If we went that far AND that we didn't expect more closing characters,
    // that means the string is balanced.
    return stack.length === 0
}

// The boring stuff: reading and printing.
//
function processData(input) {
    var res = checkDelimiters(input);
    console.log(res ? 'True' : 'False');
}

process.stdin.resume()
process.stdin.setEncoding('ascii')
var _input = ''
process.stdin.on('data', function (input) {
    _input += input
})

process.stdin.on('end', function () {
   processData(_input)
})