Neetcode: Valid Parentheses

Instructions

You are given a string s consisting of the following characters: '(', ')', '{', '}', '[' and ']'.

The input string s is valid if and only if:

Every open bracket is closed by the same type of close bracket.
Open brackets are closed in the correct order.
Every close bracket has a corresponding open bracket of the same type.

Return true if s is a valid string, and false otherwise.

Example 1:

Input: s = "[]"

Output: true

Example 2:

Input: s = "([{}])"

Output: true

Example 3:

Input: s = "[(])"

Output: false

Explanation: The brackets are not closed in the correct order.

Constraints:

1 <= s.length <= 1000

Solutions

JavaScript

class Solution {
    OPEN_PARENS;
    PAREN_MAP = {
        ')': '(',
        ']': '[',
        '}': '{',
    };

    constructor() {
        this.OPEN_PARENS = new Set(Object.values(this.PAREN_MAP))
    }

    /**
     * @param {string} s
     * @return {boolean}
     */
    isValid(s) {
        const parens = [];

        for (const char of s) {
            if (parens.length === 0 && !this.OPEN_PARENS.has(char)) {
                return false;
            }

            const lastParen = parens.at(-1);
            if (parens.length > 0 && lastParen === this.PAREN_MAP[char]) {
                parens.pop();
                continue;
            }

            parens.push(char);
        }

        return parens.length === 0;
    }
}

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