LeetCode in Kotlin

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

class Solution {
    fun isValid(s: String): Boolean {
        val stack = ArrayDeque<Char>()
        for (element in s) {
            val c = element
            if (c == '(' || c == '[' || c == '{') {
                stack.addLast(c)
            } else if (c == ')' && stack.isNotEmpty() && stack.last() == '(') {
                stack.removeLast()
            } else if (c == '}' && stack.isNotEmpty() && stack.last() == '{') {
                stack.removeLast()
            } else if (c == ']' && stack.isNotEmpty() && stack.last() == '[') {
                stack.removeLast()
            } else {
                return false
            }
        }
        return stack.isEmpty()
    }
}

This site is open source. Improve this page.