394. 字符串解码

我自己写的方法

class Solution {
    public String decodeString(String s) {
        char[] chs = s.toCharArray();
        LinkedList<Character> stack = new LinkedList<>();

        for(char ch:chs){
            if(ch==']'){
            stack = helper(stack);
            }else{
                stack.push(ch);
            }
        }

        //stack变成字符串
        String str ="";

        while(!stack.isEmpty()){
          str = stack.pop()+str;
        }
        return str;

    }

    public  LinkedList<Character> helper( LinkedList<Character> stack){
       ArrayList<Character> list = new ArrayList<>();
       while(stack.peek()!='['){
           list.add(stack.pop());
       }
       stack.pop();
      //取数字
     String a="";
      while(!stack.isEmpty()&&stack.peek()>='0'&&stack.peek()<='9'){
          a = stack.pop()+a;
      }
      int ans = Integer.parseInt(a);


       for(int i=0;i<ans;i++){
         for(int j = list.size()-1;j>=0;j--){
             stack.push(list.get(j));
         }
       }

       return stack;
    }
}

730.统计不同回文子序列