牛客网：NC26 括号生成

 
import java.util.ArrayList;
 
/**
 * @author xienl
 * @description 括号生成
 * @date 2022/7/5
 */
 
public class Solution {
    public static void main(String[] args) {
        Solution solution = new Solution();
        System.out.println(solution.generateParenthesis(3).toString());
    }
 
    public ArrayList<String> generateParenthesis (int n) {
        // write code here
       if (n == 0){
           return new ArrayList<>();
       }
 
       ArrayList<String> res =  new ArrayList<>();
       bfs(res,  "", 3,0 , 0);
       return res;
    }
 
    private void bfs(ArrayList<String> res, String sb, int n, int left, int right){
        if (left == n && right == n){
            res.add(sb);
            return;
        }
        if (left < n){
            bfs(res, sb + "(", n,left + 1, right);
        }
 
        if (right < n && left > right){
            bfs(res, sb + ")", n , left, right + 1);
        }
    }
}