https://leetcode.com/problems/decode-string/public class Solution {    private String s;    private int newPos;        public String decodeString(String ins) {        s = '.' + ins + ']';        newPos = 0;        String outStr = impl(1, 0);        return outStr.substring(1, outStr.length());    }        private String impl(int prefix, int startPos) {        int base = 0;        String baseStr = "";        String outStr = "";                for (int i=startPos; i