Generate Parentheses

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

For example, given n = 3, a solution set is:

"((()))", "(()())", "(())()", "()(())", "()()()"

 

public class Solution {
    public ArrayList<String> generateParenthesis(int n) {
        ArrayList<String> res = new ArrayList<String>();
        StringBuilder sb = new StringBuilder();
        DFS(n,n,sb,res);
        return res;
    }
    public void DFS(int leftRem,int rightRem,StringBuilder sb,ArrayList<String> res){
        if(leftRem==0 && rightRem==0){
            res.add(sb.toString());
            return;
        }
        if(leftRem>0){
            sb.append('(');
            DFS(leftRem-1,rightRem,sb,res);
            sb.deleteCharAt(sb.length()-1);
        }
        if(rightRem>leftRem){
            sb.append(')');
            DFS(leftRem,rightRem-1,sb,res);
            sb.deleteCharAt(sb.length()-1);
        }
    }
}