Exercise: brackets

Write a function func balanced(s string) bool that checks the brackets in the string s. It returns true if every bracket (, [ or { is closed later by a bracket of the same kind, every closing bracket has a pair, and the pairs do not cross.

• balanced("{[()()]}") → true
• balanced("([)]") → false
• balanced("())") → false

Constraints: s holds from 0 to 1000 characters; the function skips every character other than the six brackets; it returns true for an empty string and false for an unclosed or extra bracket.

Do not add extra imports unless the task says so explicitly.