Най-кратка поредица от пътища

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <set>
#include <unordered_map>
#include <queue>


using namespace std;

unordered_map<int, vector<int>> graph;

long long find(const vector<int>& priorities, int start, int maxPriority){
    queue<pair<long long, pair<int, int>>> pq;
    //sum, index, inSearchFor
    set<int> inCurrSearch;
    int searching = 1;
    pq.push({0, {start, 1}});

    while(!pq.empty()){
        long long currSum = pq.front().first;
        int currIndex = pq.front().second.first;
        pq.pop();

        if(inCurrSearch.find(currIndex) != inCurrSearch.end())
            continue;
        inCurrSearch.insert(currIndex);

        if(priorities[currIndex] == searching){
            if(searching == maxPriority)
                return currSum;
            searching++;
            inCurrSearch.clear();
            while(!pq.empty())
                pq.pop();
        }

        for(int neigh : graph[currIndex]){
            if(priorities[neigh] > searching)
                continue;
            pq.push({currSum + 1, {neigh, searching}});
        }


    }
    return -1;
}

int main() {
    int n, m, a, b, p, k;
    cin >> n >> m;
    vector<int> priorities(n, 0);

    for(int i = 0; i < m; i++){
        cin >> a >> b;
        graph[a].push_back(b);
        graph[b].push_back(a);
    }
    cin >> p;
    int start = 0;

    for(int i = 1; i <= p; i++){
        cin >> a;
        if(i == 1)
            start = a;
        priorities[a] = i;
    }

    cin >> k;
    for(int i = 1; i <= k; i++){
        cin >> a;
        priorities[a] = p + 1;
    }
    cout << find(priorities, start, p);
    return 0;
}