Q:

Given a string 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.

Note that an empty string is also considered valid.

Example 1:

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Input: "()"
Output: true

Example 2:

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Input: "()[]{}"
Output: true

Example 3:

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Input: "(]"
Output: false

Example 4:

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Input: "([)]"
Output: false

Example 5:

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Input: "{[]}"
Output: true
``` 

## A:
``` js
/**
 * @param {string} s
 * @return {boolean}
 */
var isValid = function(s) {
    var sl = s.length;
    while (sl > 0) {
        s = s.replace('{}', '')
        s = s.replace('[]', '')
        s = s.replace('()', '')

        sl--;
    }
    
    return s == '';
};

Appendix:

Tricks about regex:

1. Most common flags :
   • i : case insensitive
   • g : global (doesn’t stop after first match)
   • m : multi-line
2. Most common anchors :
   • ^ : Start of string
   • $ : End of string
   • \A : Start of string (not affected by multi-line content)
   • \Z : End of string (not affected by multi-line content)
3. Most common quantifiers :
   • {n} : Exactly n times
   • {n,} : At least n times
   • {m,n} : Between m and n times
   • ? : Zero or one time
   • + : One or more times
   • * : Zero, one or more times
4. Most common meta sequences :
   • . : Any character but \n and \r
   • \w | \W : Any word character | Any non-word character
   • \d | \D : Any digit character | Any non-digit character
   • \s | \S : Any whitespace character | Any non-whitespace character
5. Character set :
   • [abc] : Will match either a, b or c
   • [1-9] : Will match any digit from 1 to 9
   • [a-zA-Z] : Will match any letter
6. Match any character but :
   • [^abc] : Matches anything but a, b or c
7. Escape a character :
   • \character (example : escaping + => +)
8. Refer to a group (also used for capturing groups, look further):
   • (group of characters) (example : /(he)+/ will match ‘hehehe’
9. One group or another :
   • | : /^h((ello)|(ola))$/ will match both ‘hello’ and ‘hola’