Generate Parantheses in Swift

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

A parentheses string is well-formed if and only if:

• It is the empty string, or

• It can be written as AB (A concatenated with B), where A and B are well-formed, or

• It can be written as (A), where A is well-formed.

Example 1:

Input: n = 3
Output: ["((()))","(()())","(())()","()(())","()()()"]

Example 2:

Input: n = 1
Output: ["()"]

Note: 1 <= n <= 8