import scala.collection.mutable

​

object Solution extends App // Initialize hash map with mappings. This simply makes the code easier to read.

{

  var mappings = new mutable.HashMap[Char, Char]

  this.mappings.put(')', '(')

  this.mappings.put('}', '{')

  this.mappings.put(']', '[')

​

  var reversedMappings = new mutable.HashMap[Char, Char]

  this.reversedMappings.put('(', ')')

  this.reversedMappings.put('{', '}')

  this.reversedMappings.put('[', ']')

  // Hash table that takes care of the mappings.

​

​

  def isValid(s: String): Boolean = { // Initialize a stack to be used in the algorithm.

    val stack = new mutable.Stack[Char]()

    for (i <- 0 until s.length) {

      val c = s.charAt(i)

      // If the current character is a closing bracket.

      if (mappings.contains(c)) { // Get the top element of the stack. If the stack is empty, set a dummy value of '#'

        var topElement:Char = '0'

        if (stack.isEmpty)

          topElement = '#'

        else topElement = stack.pop

        // If the mapping for this bracket doesn't match the stack's top element, return false.

        if (topElement != mappings(c))

          return false

      }

      else if(reversedMappings.contains(c)) { // If it was an opening bracket, push to the stack.

        stack.push(c)

      }

    }

    // If the stack still contains elements, then it is an invalid expression.

    stack.isEmpty

  }

​

​

  val string = "let output = function () { console.log('Anonymous function'); };"

  println(isValid(string))

}