LeetCode-in-All

20. Valid Parentheses

Easy

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.

Example 1:

Input: s = “()”

Output: true

Example 2:

Input: s = “()[]{}”

Output: true

Example 3:

Input: s = “(]”

Output: false

Example 4:

Input: s = “([)]”

Output: false

Example 5:

Input: s = “{[]}”

Output: true

Constraints:

• 1 <= s.length <= 104
• s consists of parentheses only '()[]{}'.

Solution

import scala.collection.mutable.Stack
import scala.util.control.Breaks._

object Solution {
    def isValid(s: String): Boolean = {
        val stack = Stack[Char]()
        var result = true

        breakable {
            for (i <- 0 until s.length) {
                val c = s.charAt(i)
                if (c == '(' || c == '[' || c == '{') {
                    stack.push(c)
                } else if (c == ')' && stack.nonEmpty && stack.top == '(') {
                    stack.pop()
                } else if (c == '}' && stack.nonEmpty && stack.top == '{') {
                    stack.pop()
                } else if (c == ']' && stack.nonEmpty && stack.top == '[') {
                    stack.pop()
                } else {
                    result = false
                    break()
                }
            }
        }

        result && stack.isEmpty
    }
}

This site is open source. Improve this page.