Monistus

input/code.cpp: In function 'int main()':
input/code.cpp:46:14: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   46 |     while (i < input.length()) {
      |            ~~^~~~~~~~~~~~~~~~

#include <string>
#include <vector>
#include <iostream>

using ip = std::pair<int, int>;

struct scope {
    int idx;
    int end;
    int offset;
};

void recurse(std::string const& input, std::vector<scope> stack, int i, int length) {
    scope s = scope(i, i+length, 0);

    while (length > 0) {
        for (int stack_i = stack.size()-1; stack_i >= 0; --stack_i) {
            if (i >= stack[stack_i].end-stack[stack_i].offset) {
                s.offset += stack[stack_i].end - stack[stack_i].idx;
                i = stack[stack_i].idx;
            }
        }

        if (input[i] >= '1' && input[i] <= '9') {
            stack.push_back(s);

            recurse(input, stack, i+1, input[i] - int('0'));

            stack.pop_back();
        } else {
            std::cout << input[i];
        }

        --length;
        ++i;
    }
}

int main() {
    std::string input;

    std::cin >> input;
    std::vector<scope> stack;

    int i = 0;
    while (i < input.length()) {
        for (int j = stack.size()-1; j >= 0; --j) {
            if (i >= stack[i].end) {
                i = stack[i].idx;
                j = stack.size();
            }
        }
        if (input[i] >= '1' && input[i] <= '9') {
            recurse(input, stack, i+1, input[i] - int('0'));
        } else {
            std::cout << input[i];
        }
        ++i;
    }

    std::cout << std::endl;

    return 0;
}

Test 1

Group: 1, 2

Verdict: ACCEPTED

Test 2

Group: 1, 2

Verdict: ACCEPTED

Test 3

Group: 1, 2

Verdict: ACCEPTED

Test 4

Group: 1, 2

Verdict: ACCEPTED

Test 5

Group: 1, 2

Verdict: ACCEPTED

Test 6

Group: 1, 2

Verdict: ACCEPTED

Test 7

Group: 1, 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: RUNTIME ERROR

Test 10

Group: 2

Verdict: RUNTIME ERROR

Test 11

Group: 2

Verdict: ACCEPTED

Test 12

Group: 2

Verdict: ACCEPTED

Test 13

Group: 2

Verdict: ACCEPTED

Test 14

Group: 2

Verdict: ACCEPTED