20. Valid Parantheses

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 '()[]{}'.

Solutions:

JavaScript

/**
 * @param {string} s
 * @return {boolean}
 */

 const isValid = function(s) {

    let stack = [];
    let len = s.length;
    let map = {
      '(': ')',
      '[': ']',
      '{': '}'
    };

    for (let i = 0; i < len; i++) {
      if (stack.length > 0 && map[stack[stack.length - 1]] === s[i]) {
        stack.pop();
      } else {
        stack.push(s[i]);
      }
    }

    return stack.length == 0;
    
  };