runner.cpp

#include <bits/stdc++.h>
 
using namespace std;
 
unsigned char tape[300000] = {0};
unsigned char* ptr = tape;
 
void interpret(const char* input)
{
    char current_char;
    unsigned int i, loop;
    
    for (i = 0; input[i] != 0; ++i)
    {
        current_char = input[i];
 
        switch (current_char)
        {
            case '>':
                ++ptr;
                break;
            case '<':
                --ptr;
                break;
            case '+':
                ++*ptr;
                break;
            case '-':
                --*ptr;
                break;
            case '.':
                putchar(*ptr);
                break;
            case ',':
                *ptr = getchar();
                break;
            case '[':
                if (*ptr == 0)
                {
                    loop = 1;
                    while (loop > 0)
                    {
                        current_char = input[++i];
                        if (current_char == '[')
                            loop++;
                        else if (current_char == ']')
                            loop--;
                    }
                }
                break;
            case ']':
                if (*ptr)
                {
                    loop = 1;
                    while (loop > 0)
                    {
                        current_char = input[--i];
                        if (current_char == '[')
                            loop--;
                        else if (current_char == ']')
                            loop++;
                    }
                }
        }
    }
}
 
char dict[8] = {'-', '>', '.', ']', '<', '+', '[', ','};
 
int mod(string num, int a)
{
    int res = 0;
 
    for (int i = 0; i < num.length(); i++)
        res = (res * 10 + num[i] - '0') % a;
 
    return res;
}
 
string longDivision(string number, int divisor) 
{ 
    string ans; 
  
    int idx = 0; 
    int temp = number[idx] - '0'; 
    while (temp < divisor) 
        temp = temp * 10 + (number[++idx] - '0'); 
   
    while (number.size() > idx) { 
        ans += (temp / divisor) + '0'; 
  
        temp = (temp % divisor) * 10 + number[++idx] - '0'; 
    } 
      if (ans.length() == 0) 
        return "0"; 
  
    return ans; 
} 
 
void decode(string code) {
    string brainfuck = "";
    int p = 2;
    while (code != "1") {
        int op = 0;
        while (!mod(code, p)) {
            op++;
            code = longDivision(code, p);
        }
        p++;
        if (!op) continue;
        brainfuck += dict[op - 1];
    }
    interpret(brainfuck.c_str());
}
 
int main() {
    string code;
    cin >> code;
    decode(code);
}