Elevator Trouble

#include <bits/stdc++.h>

using namespace std;

int main() {
    cin.sync_with_stdio(false);
    int floors, start, goal, u, d;
    cin >> floors >> start >> goal >> u >> d;

    // each pair contains the current position and
    // also a set of all visited positions so we
    // can terminate the search when the current position
    // is already in the visited ones
    queue<pair<int, set<int>>> to_visit;
    int shortest = -1;

    to_visit.push(make_pair(start, set<int>()));

    while (to_visit.size() > 0) {
        // pop a pair from stack
        auto elem = to_visit.front();
        to_visit.pop();

        // check if the current position is goal

        if (elem.first == goal) {
            // if it is, we are done
            shortest = elem.second.size() + 1;
            break;
        }

        // check if current position is invalid
        if (elem.first < 1 || elem.first > floors) {
            // if true, continue
            continue;
        }

        // check if the current position is already in the set
        if (elem.second.count(elem.first)) {
            // if it is, continue
            continue;
        }

        // create a new set for both children where the current position is added
        set<int> newset = elem.second;
        newset.insert(elem.first);

        // push the two child nodes
        to_visit.push(make_pair(elem.first + u, newset));
        to_visit.push(make_pair(elem.first + d, newset));
    }

    if (shortest == -1) {
        cout << "use the stairs\n";
    } else  {
        cout << shortest << "\n";
    }

}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: RUNTIME ERROR

Test 4

Verdict: TIME LIMIT EXCEEDED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: TIME LIMIT EXCEEDED

Test 7

Verdict: WRONG ANSWER

Test 8

Verdict: RUNTIME ERROR

Test 9

Verdict: ACCEPTED

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: RUNTIME ERROR

Test 12

Verdict: ACCEPTED