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:

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

 

Constraints:

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

Solution

/**
 * @param {string} s
 * @return {boolean}
 */
var isValid = function(s) {
    const stack = [];
    const pairs = {
        "(" : ")",
        "{" : "}",
        "[" : "]"
    }
    for (const i of s) {
        if (i in pairs) {
            stack.push(i);
        } else if (j = stack.pop()) {
            if (pairs[j] !== i) {
                return false
            }
        } else {
            return false;
        }
    }
    return !stack.length
};

Verify if the given string s is valid by storing the left brackets in a stack stack and popping the top to test if it matches the corresponding right bracket.