Return true if parentheses in list chars are balanced.
1
2
3
4
| scala> balance("(foo (bar))".toList)
res1: Boolean = true
scala> balance("(foo bar".toList)
res2: Boolean = false
|
1
2
3
4
5
6
7
8
9
10
| def balanceLeft(chars: List[Char], left: Int): Boolean = chars match {
case Nil => left == 0
case _ => chars.head match {
case ')' => left > 0 && balanceLeft(chars.tail, left - 1)
case '(' => balanceLeft(chars.tail, left + 1)
case _ => balanceLeft(chars.tail, left)
}
}
def balance(chars: List[Char]): Boolean = balanceLeft(chars, 0)
|