algorithm - Scala code to check if parenthesis are balanced -

i'm writing scala function check balanced parentheses. "()","([]{})" both balanced, ")","(){[}]" aren't balanced

below code wrote should working. have no idea why say's false inputs try.

package general  import scala.collection.mutable.stack import scala.collection.immutable.hashmap  object balanceparen {     def main(args: array[string]) {         print(isbalanced("()"));     }     def isbalanced(input: string): boolean = {         val stack = new stack[char]         val brace = hashmap('(' -> ')', '[' -> ']', '{' -> '}')          input map (( ch: char ) => {             if( brace contains ch ) stack push ch             else {                 if( brace.isempty )              return false                 if( brace.get(stack.pop) != ch ) return false             }         })         return stack.isempty     } } 

hashmap's get method returns option, test needs change like:

if( brace.get(stack.pop) != some(ch) ) return false 

or:

if( brace.get(stack.pop).contains(ch) ) return false