Dijkstra's Shortest Path Algorithm

Question

Is there anything I could do better in this Dijkstra's Implementation. This is my implementation of Dijkstra after understanding the concept. I used hash table wherever possible to have faster access

#include <iostream>
#include <unordered_map>
#include <vector>
using namespace std;
string lowestnode(unordered_map<string,int> &costs, vector<string> &processed);
int main(){
 //Finding Shortest Path from 'S' to 'F'
 unordered_map<string,unordered_map<string, int>> graph;
 graph["S"] = {make_pair("A", 6), make_pair("B", 2)};
 graph["A"] = {make_pair("F", 1)};
 graph["B"] = {make_pair("A", 3), make_pair("F", 5)};
 graph["F"] = {};
 unordered_map<string, int> costs;
 costs["A"] = 6;
 costs["B"] = 2;
 costs["F"] = INT_MAX;
 unordered_map<string, string> parents;
 parents["A"] = "S";
 parents["B"] = "S";
 parents["F"] = "None";
 vector<string> processed;
 processed.reserve(4);
 string node = lowestnode(costs, processed);
 while(node != ""){
 int cost = costs[node];
 unordered_map<string, int> neighbours;
 neighbours = graph[node];
 for (auto neighbour : neighbours){
 int newcost = cost + neighbour.second;
 if(costs[neighbour.first] > newcost){
 costs[neighbour.first] = newcost;
 parents[neighbour.first] = node;
 }
 }
 processed.push_back(node);
 node = lowestnode(costs, processed);
 }
 cout<<"Costs : ";
 for (auto cost : costs){
 cout<<"[ "<<cost.first<<":"<<cost.second<<" ] ";
 }
 
 //'F' is the final Destination
 string answer = "F";
 string child = "F";
 while(parents[child] != ""){
 answer += parents[child];
 child = parents[child];
 }
 cout<<"\nPath : ";
 for (int i=answer.size()-1; i>=0; i--){
 cout<<answer[i];
 if(i!= 0) cout<<" -> ";
 }
}
string lowestnode(unordered_map<string,int> &costs, vector<string> &processed){
 string minnode = "";
 int minvalue = INT_MAX;
 for (auto node : costs){
 int flag = 0;
 for (auto visited : processed){
 if(node.first == visited){
 flag = 1;
 break;
 }
 }
 if(flag) continue;
 if(minvalue > node.second){
 minvalue = node.second;
 minnode = node.first;
 }
 }
 return minnode;
}

• Toby Speight: Avoid using namespace std;
• Oliver Schönrock: Dykstra's is normally implemented with a priority queue, and even though the c++ std::priority_queue does not allow element modification, it is easy to "keep pushing" and discard stale entries on pop. You should research this approach as it is quite canonical I think.