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{ Bracket
Balancing }

The Question

One of your colleagues insists on writing all code in Notepad, resulting in code that won't run because the brackets, braces, and parenthesis are not properly balanced. You decide to write a bracket validator to check whether the brackets /braces/ parenthesis are valid.

Notes

• You have already written a RegEx to get rid of the non-brackets from the input string (i.e. your input will be all brackets, parenthesis, and braces)
• For the purpose of the problem these are considered 'brackets': 

​[ ] ( ) { }

What you need to do:

Consider these to be valid pairs:

​[  and   ] 

(   and   ) 

{   and  } 

Write an efficient function that tells us whether or not an input string's brackets are properly nested.

"{ [ ] ( ) }" should return true

"{ [ ( ] ) }" should return false

"{ [ }" should return false

"{ [ ( [ { ( )[ ]{ } } ] ) ] }" should return true

Approach

• You have "opening"- ( { [ - and closing - ) { ] - brackets
• Each closing bracket should correspond to the nearest opening bracket that it pairs with
• Every opening and closing bracket should be in a pair

Possible Solution

function hasBalancedBrackets(inputString) {
	var inputBrackets = inputString.match(/[[\](){}]/g);
	var bracketPairs = {  
		'[' : ']',
		'(' : ')',
		'{' : '}'
	}; 
	var brackets = [ ];
	if (!inputString.length || !inputBrackets.length) 
	        return true;
	inputBrackets.forEach (function (bracket) {
		var lastBracket = brackets[brackets.length - 1];
		if (bracketPairs[lastBracket] === bracket) 
			brackets.pop(); 
		else 
			brackets.push(bracket);
	});

	return brackets.length === 0; 
}

Possible Solution

function hasBalancedBrackets(inputString){
      var braces = inputString.match(/[[\](){}]/g);
      var e;

      while ((e = /\(\)/.exec(braces)) || (e = /\[\]/.exec(braces)) || (e = /\{\}/.exec(braces))) 
      {
            braces = braces.replace(e[0], '');
      }

      return !braces;
}

Conclusion  

REPL.IT solutions

- Data structure principles can come in handy even when you are not explicitly creating a certain structure

-You can use arrays and array methods in Javascript to create an array that basically behaves like a stack/queue