Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.
Example 1:
Input: n = 3
Output: ["((()))","(()())","(())()","()(())","()()()"]
Example 2:
Input: n = 1
Output: ["()"]
Constraints:
- 1 <= n <= 8
class Solution {
public List<String> generateParenthesis(int n) {
List<String> list = new ArrayList<>();
backtrack(list,"",0,0,n);
return list;
}
public void backtrack(List<String> list,String str, int left ,int right,int n){
// 正好遍历结束，结果放入队列
if(str.length()==n*2){
list.add(str);
return;
}
// 左括号<n
if(left<n){
backtrack(list,str+"(",left+1,right,n);
}
// 右括号<左括号
if(right<left){
backtrack(list,str+")",left,right+1,n);
}
}
}