A common problem in parsing computer languages and compiler implementations is determining if an input string is balanced. That is, a string can be considered balanced if for every opening element ( (, [, <, etc) there is a corresponding closing element ( ), ], >, etc).
Today, we’re interested in writing a method that will determine if a String is balanced. Write a method, isBalanced(String s) that returns true if every opening element is matched by a closing element of exactly the same type. Extra opening elements, or extra closing elements, result in an unbalanced string. For this problem, we are only interested in three sets of characters -- {, (, and [ (and their closing equivalents, }, ), and ]). Other characters, such as <, can be skipped. Extra characters (letters, numbers, other symbols) should all be skipped. Additionally, the ordering of each closing element must match the ordering of each opening element. This is illustrated by examples below.
The following examples illustrate the expected behaviour:
is Balanced ("{{mustache templates use double curly braces}}") should return true
is Balanced("{{but here we have our template wrong!}") should return false
is Balanced("{ ( ( some text ) ) }") should return true
is Balanced("{ ( ( some text ) } )") should return false (note that the ordering of the last two elements is wrong)
Write an implementation that uses one or more Stacks to solve this problem. As a client of the Stack class, you are not concerned with how it works directly, just that it does work.