AtomicKotlinCourse/Usability/when Expressions/Exercise 3/task.md

when Expressions (#3)

Implement the function isBalanced that takes an argument of a string consisting of parentheses like ()(()) and checks whether each opening symbol has a corresponding closing symbol and the pairs of parentheses are properly nested.

An input string can contain whitespaces which should be ignored. If it contains any other characters besides parentheses and whitespaces, IllegalArgumentException should be thrown.

Some examples:

• () is balanced
• (() is unbalanced
• )( is unbalanced
• ( ()() ) is balanced
• *() leads to IllegalArgumentException

Iterate over the string and count the number of left braces which are unmatched on each step. At the end, this number should be 0. If it is less than zero at some point, the string is unbalanced.