Balanced Brackets

Write a function that takes a string of brackets and checks whether they're balanced or not.

The sequence is balanced if:

• It contains no unmatched brackets.
• The subset of brackets enclosed within the confines of a matched pair of brackets is also balanced.

Examples

isBalanced("{[()]}") ➞ True

isBalanced("[()]{}") ➞ True

isBalanced("{[([)]]}") ➞ False

Notes

Return None if no input is given.