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[LeetCode 20] Valid Parentheses

Problem

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

An input string is valid if:

Open brackets must be closed by the same type of brackets. 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 '()[]{}'.

Typescript

function isValid(s: string): boolean {
    if(s.length % 2 === 1) return false;

    const stack = []
    const leftBrackets = ['(', '[', '{']

    for(let p of s) {
        // push to stack if it is left brackets
        if(leftBrackets.includes(p)) {
            stack.push(p)
        } else {
            // pop if it is right brackets and do order check
            const current = stack.pop()
            if(!(
                (p === ')' && current === '(') ||
                (p === ']' && current === '[' ) ||
                (p === '}' && current === '{')
            )
            ){
                return false;
            }
        }
    }

    // there maybe only left brackets
    return stack.length === 0;
};

Reference