Answer to an interview question

validateBrackets.js

let opening = ['{', '[', '('];
let closing = ['}', ']', ')'];
let all = opening.concat(closing)

function validate(s) {
  if (s.length == 0) return true;

  // ignore unknown chars at the head
  while (all.indexOf(s.charAt(0)) == -1) {
    s = s.slice(1);
    if (s.length == 0) return true;
  }

  let startToken = s.charAt(0);
  let endToken = closing[opening.indexOf(startToken)];
  let accm = "";
  let pointer = 1;
  let seen = 1

  if (!endToken) return false;

  for (; pointer < s.length; pointer++) {
    if (s.charAt(pointer) == startToken) {
      seen++;
    } else if (s.charAt(pointer) == endToken) {
      seen--;
    }

    if (seen == 0) {
      break;
    }

    accm = accm + s.charAt(pointer);
  }

  // we're balanced, the area between our boundaries is valid, as is the rest
  return seen == 0 && validate(accm) && validate(s.slice(pointer + 1));
}

let tests = [
    "", "{", "}", "{}", "}{",
    "{{}", "{}}", "{{}}", "}{}", "{}{",
    "([{}])", "([{})]",
    "{abc}", "abc{", "}abc",
    "var a = function(){return 'b';}",
    "var a = function(){return 'b';"
];

let results = [
  true, false, false, true, false,
  false, false, true, false, false,
  true, false,
  true, false, false,
  true,
  false
]

var fail = false;

for (let i = 0; i < tests.length; i++) {
  if (validate(tests[i]) != results[i]) {
    console.log("Test Failure: " + tests[i]);
    fail = true;
  }
}

if (!fail) {
  console.log("All tests passed.");
}