LeetCode Problem
https://leetcode.com/problems/generateparentheses/
Given n
pairs of parentheses, write a function to generate all combinations of wellformed parentheses.
For example, given n = 3, a solution set is:

Explanation
This is a classic recursive problem, in each recursive loop, we need to add one char (
or )
to current state, but with two limitations:
The number of (
and )
in the final state should be equal n
.
In any state, the number of )
should be less or equal to (
.
So we use these parameters in recursive function:
ll
: limit number of (
lr
: limit number of )
