Leetcode22. Generate Parentheses

package leetcode2;

import java.util.ArrayList;

public class Generate_parenthese {
    public static ArrayList<String> generateParenthesis(int n) {
        ArrayList<String> reArrayList=new ArrayList<String>();
        String s=new String();
        dfs(reArrayList,s,n,n); //DFS的模版递归 dfs(list<E>,E,deep,somethingConstant)
        return reArrayList;
    }

   public static void dfs(ArrayList<String> reArrayList, String s, int left,int right) {
        // TODO Auto-generated method stub
        // 先考虑deep极值,此处为left，right个数,直接return
       if(right<left){
           return;
       }
       if(left==0&&right==0){  //当括号都用完时，将s存入list中
           reArrayList.add(s);
           return;
       }
       if(left>0){
           dfs(reArrayList, s+‘(‘, left-1, right);
       }
       if(right>0){
           dfs(reArrayList, s+‘)‘, left, right-1);
       }
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        System.out.println(generateParenthesis(3));
    }

}