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| 1 | +package ValidParentheses_p20 |
| 2 | + |
| 3 | +import scala.collection.mutable.Stack |
| 4 | + |
| 5 | +/** |
| 6 | + * https://leetcode.com/problems/valid-parentheses/ |
| 7 | + * Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', |
| 8 | + * determine if the input string is valid. |
| 9 | + * An input string is valid if: |
| 10 | + * Open brackets must be closed by the same type of brackets |
| 11 | + * Open brackets must be closed in the correct order. |
| 12 | + * |
| 13 | + * @tags: easy |
| 14 | + */ |
| 15 | +object Solution { |
| 16 | + |
| 17 | + val OpenToClose: Map[Char, Char] = Map('{' -> '}', '[' -> ']', '(' -> ')') |
| 18 | + val CloseToOpen: Map[Char, Char] = OpenToClose.map(_.swap) |
| 19 | + |
| 20 | + def main(args: Array[String]): Unit = { |
| 21 | + println(!isValid("[")) |
| 22 | + println(isValid("()[]{}")) // all should be true |
| 23 | + println(isValid("()")) |
| 24 | + println(!isValid("(]")) |
| 25 | + println(isValid("[()]")) |
| 26 | + println(isValid("{[()]}")) |
| 27 | + println(isValid("([{{[(())]}}])")) |
| 28 | + println(!isValid("{{[]()}}}}")) |
| 29 | + println(!isValid("{{[](A}}}}")) |
| 30 | + println(!isValid("{[(])}")) |
| 31 | + } |
| 32 | + |
| 33 | + def isValid(s: String): Boolean = { |
| 34 | + stackParenthesisSolution(s) // Stack Solution |
| 35 | + //parenthesesAreBalanced(s) // Tail recursion solution |
| 36 | + } |
| 37 | + |
| 38 | + import scala.collection.mutable.Stack |
| 39 | + /** |
| 40 | + * Stack solution |
| 41 | + */ |
| 42 | + def stackParenthesisSolution(s: String): Boolean = { |
| 43 | + val stack = new Stack[Char]() |
| 44 | + if (s.size == 0) stack.push('f') |
| 45 | + |
| 46 | + s.foreach(char => { |
| 47 | + if (OpenToClose.contains(char)) { |
| 48 | + stack.push(char) |
| 49 | + } else { |
| 50 | + if (stack.size > 0 && OpenToClose.get(stack.top) == Some(char)) |
| 51 | + stack.pop() |
| 52 | + else |
| 53 | + stack.push('f') |
| 54 | + } |
| 55 | + }) |
| 56 | + |
| 57 | + stack.size == 0 |
| 58 | + } |
| 59 | + |
| 60 | + /** |
| 61 | + * Tail recursion solution |
| 62 | + * is taken from https://www.scala-algorithms.com/ParenthesesTailRecursive/ |
| 63 | + * |
| 64 | + * @param |
| 65 | + * @return |
| 66 | + */ |
| 67 | + def parenthesesAreBalanced(s: String): Boolean = { |
| 68 | + if (s.isEmpty) true |
| 69 | + else { |
| 70 | + @scala.annotation.tailrec |
| 71 | + def go(position: Int, stack: List[Char]): Boolean = { |
| 72 | + if (position == s.length) stack.isEmpty |
| 73 | + else { |
| 74 | + val char = s(position) |
| 75 | + val isOpening = OpenToClose.contains(char) |
| 76 | + val isClosing = CloseToOpen.contains(char) |
| 77 | + if (isOpening) go(position + 1, char :: stack) |
| 78 | + else if (isClosing) { |
| 79 | + val expectedCharForMatching = CloseToOpen(char) |
| 80 | + stack match { |
| 81 | + case `expectedCharForMatching` :: rest => |
| 82 | + go(position + 1, rest) |
| 83 | + case _ => |
| 84 | + false |
| 85 | + } |
| 86 | + } else false |
| 87 | + } |
| 88 | + } |
| 89 | + |
| 90 | + go(position = 0, stack = List.empty) |
| 91 | + } |
| 92 | + } |
| 93 | +} |
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