Shortest tour

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <unordered_map>
#include <unordered_set>

#include <queue>

using namespace std;

unordered_map<int, vector<int>> graph;

int find(vector<int>& priorities, int prioritiesCount, int start){
    int searchFor = 1;
    int sum = 0;

    priority_queue<pair<int, pair<int, int>>, vector<pair<int, pair<int, int>>>, greater<>> next;
    //sumSoFar, index, AddedInSearchFor

    unordered_set<int> inCurrentSearch;
    next.push({0, {start, 1}});

    while(!next.empty()){
        auto current = next.top();
        next.pop();

        int currSumSoFar = current.first;
        int currIndex = current.second.first;
        if(inCurrentSearch.find(currIndex) != inCurrentSearch.end())
            continue;

        inCurrentSearch.insert(currIndex);

        if(priorities[currIndex] == searchFor){
            if(searchFor == prioritiesCount)
                return currSumSoFar;
            searchFor++;
            inCurrentSearch.clear();
        }

        for(int neighbour : graph[currIndex]){
            if(priorities[neighbour] > searchFor){
                continue;
            }
            next.push({currSumSoFar + 1, {neighbour, searchFor}});
        }

        while(!next.empty() && next.top().second.second < searchFor)
            next.pop();
    }
    return -1;
}

int main() {
    int n, m, a, b, k;
    cin >> n >> m;
    vector<int> priorities(n, -1);
    for(int i = 0; i < m; i++){
        cin >> a >> b;
        if (a == b)
           continue;
        graph[a].push_back(b);
    }
    cin >> k;
    int start = 0;
    for(int i = 1; i <= k; i++){
        cin >> a;
        if(i == 1)
            start = a;
        priorities[a] = i;
    }

    cout << find(priorities, k, start);

}