双栈法

  public String decodeString(String s) {String res = "";Stack<Integer> countStack = new Stack<>();Stack<String> resStack = new Stack<>();int idx = 0;while (idx < s.length()){char cur = s.charAt(idx);//处理数字if(Character.isDigit(cur)){StringBuffer ret = new StringBuffer();while (Character.isDigit(s.charAt(idx))){ret.append(s.charAt(idx++));}countStack.push(Integer.parseInt(ret.toString()));} else if (cur == '[') {//处理[resStack.push(res);res = "";idx++;}else if(cur == ']'){//处理']',处理相匹配的StringBuffer temp = new StringBuffer(resStack.pop());int repeatTimes = countStack.pop();for(int i=0;i<repeatTimes;i++){temp.append(res);}res = temp.toString();idx++;}else{//处理普通字符res+=s.charAt(idx++);}}return res;}