题解 | #牛牛的字符串解码问题#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param s string字符串 
     * @return string字符串
     */
    public String decodeString (String s) {
        // write code here
        Stack<String> stack = new Stack<>();
        Stack<String> numStack = new Stack<>();
        StringBuilder res = new StringBuilder();
        for(char c : s.toCharArray()){
            if(Character.isDigit(c)){
                numStack.push(String.valueOf(c));
            }else if(c == ']'){
                StringBuilder t = new StringBuilder();
                while(!stack.isEmpty() && !stack.peek().equals("[")){
                    t.insert(0,stack.pop());
                }
                stack.pop();
                int cnt = Integer.parseInt(numStack.pop());
                String str = t.toString();
                StringBuilder t2 = new StringBuilder();
                while(cnt > 0){
                    t2.append(str);
                    cnt--;
                }
                stack.push(t2.toString());
            }else{
                stack.push(String.valueOf(c));
            }
        }

        while(!stack.isEmpty()){
            res.insert(0,stack.pop());
        }

        return res.toString();
    }
}