Hackerrank: Balanced Brackets Solution

1function Stack() {
2  const stack = []
3
4  this.push = function (el) {
5    stack.push(el)
6  }
7
8  this.pop = function () {
9    return stack.pop()
10  }
11
12  this.peek = function () {
13    return stack[stack.length - 1]
14  }
15
16  this.isEmpty = function () {
17    return stack.length === 0
18  }
19}
20
21function isBalanced(s) {
22  const isOpen = c => "{[(".includes(c)
23  const closeOf = c =>
24    ({
25      "{": "}",
26      "[": "]",
27      "(": ")",
28    }[c])
29  const stack = new Stack()
30  for (const c of s) {
31    if (isOpen(c)) {
32      stack.push(c)
33    } else if (c === closeOf(stack.peek())) {
34      stack.pop()
35    } else {
36      stack.push(c)
37    }
38  }
39
40  return stack.isEmpty() ? "YES" : "NO"
41}