22. 括号生成

package leetcode;

import java.util.ArrayList;
import java.util.List;

public class demo_22 {
    public List<String> generateParenthesis(int n) {
        List<String> list=new ArrayList<String>();
        String s="";
        //"("的个数
        int left=0;
        //")"的个数
        int right=0;
        backtrack(list, n, left, right, s);
        for(String ss:list) {
            System.out.print(ss+" ");
        }
        return list;
    }
    //深度优先生成树
    public void backtrack(List<String> list,int n,int left,int right,String s) {
        //左括号的个数不能大于右括号
        if(right>left) {return;}
        if(right==n&&left==n) {
            list.add(s);
            return;
        }
        if(left<n) {
            backtrack(list, n, left+1, right, s+"(");
        }
        if(right<n) {
            backtrack(list, n, left, right+1, s+")");
        }
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        demo_22 d22=new demo_22();
        d22.generateParenthesis(3);
    }

}