m. Decode_String.cpp

/*
Problem Link: https://practice.geeksforgeeks.org/problems/decode-the-string2444/1
Title: Decode the String
Difficulty: Easy
Author: Hariket Sukesh Kumar Sheth
Language: C++
*/

#include <bits/stdc++.h>
using namespace std;

class Solution{
public:
    string decodedString(string s){
       stack<char>st;
       string ans;
       for(int i=0;i<s.size();i++){
           if(s[i]!=']') st.push(s[i]);
           else{
               string temp;
               while(!st.empty() && st.top()!='['){
                  temp = st.top() + temp;
                st.pop();
               }
               st.pop();
            string num;
            while (!st.empty() && isdigit(st.top())) {
                num = st.top() + num;
                st.pop();
            }
            int number = stoi(num);
            string repeat;
            for (int j = 0; j < number; j++)
                repeat += temp;
            for (char c : repeat)
                st.push(c);
           }
           
       }
       string res;
    while (!st.empty()) {
        res = st.top() + res;
        st.pop();
    }
    return res;
    }
};

int main(){
    int t;
    cin>>t;
    while(t--){
        string s;
        cin>>s;
        
        Solution ob;
        cout<<ob.decodedString(s)<<"\n";
    }
    return 0;
}