[Luogu] 外星密码

#include <bits/stdc++.h>

using namespace std;
const int N = 20010;

int pre[N], hou[N];

string s;
string ss;
int main()
{
    cin >> s;
    if(s.find(‘[‘) == -1) {
        cout << s;
        return 0;
    }
    for(int T = 1; T <= 10; T ++){
        
        if(T != 1) s = ss;
        int len = s.length(), last;
        if(s.find(‘[‘) == -1) break;
        memset(hou, 0, sizeof(hou));
        bool flag;
        for(int i = 0; i < len; i ++){
            if(s[i] == ‘[‘) {last = i; flag = 1;}
            else if(s[i] == ‘]‘ && flag) {hou[last] = i; flag = 0;} 
        }
        ss.clear();
        for(int i = 0; i < len; i ++){
            if(!hou[i]) {ss += s[i]; continue ;}
            int tot = 0, j;
            j = i + 1;
            while(s[j] >= ‘0‘ && s[j] <= ‘9‘){
                tot = tot * 10 + s[j] - ‘0‘;
                j ++;
            }
            string s1;
            while(s[j] != ‘]‘) s1 += s[j ++];
            for(int k = 1; k <= tot; k ++) ss += s1;
            i = hou[i];
        }
    }
    cout << ss;
    
    return 0;
}