Java中实现解码字符串的方法，实用代码

s = "3[a]2[bc]", return "aaabcbc".
s = "3[a2[c]]", return "accaccacc".
s = "2[abc]3[cd]ef", return "abcabccdcdcdef".

class Node{
int num;
ArrayList<Node> list;
char symbol;
boolean isList;
public Node(char s){
symbol=s;
}
public Node(int n){
list = new ArrayList<Node>();
isList=true;
num=n;
}
public String toString(){
String s = "";
if(isList){
s += num + ":" + list.toString();
}else{
s += symbol;
}
return s;
}
}
public class Solution {
public String decodeString(String s) {
int i = 0;
Stack<Node> stack = new Stack<Node>();
stack.push(new Node(1));
String t = "";
while (i < s.length()) {
char c = s.charAt(i);
// new Node
if (c >= '0' && c <= '9') {
t += c;
} else if (c == '[') {
if (t.length() > 0) {
int num = Integer.parseInt(t);
stack.push(new Node(num));
t = "";
}
} else if (c == ']') {
Node top = stack.pop();
if (stack.isEmpty()) {
} else {
stack.peek().list.add(top);
}
} else {
stack.peek().list.add(new Node(c));
}
i++;
}
return getString(stack.peek());
}
public String getString(Node node){
String s="";
if(node.isList){
for(int i=0; i<node.num; i++){
for(Node t: node.list)
s+= getString(t);
}
}else{
s+=node.symbol;
}
return s;
}
}