# Program to find correct order of visited cities in C++

Suppose we have a list of airline tickets represented by pairs of departure and arrival airports like [from, to], we have to reconstruct the itinerary in correct order. All of the tickets belong to a man who departs from KLK. So, the itinerary must begin with JFK.

So if the input is like [["MUC", "LHR"], ["KLK ", "MUC"], ["SFO", "SJC"], ["LHR", "SFO"]], then the output will be ["KLK ", "MUC", "LHR", "SFO", "SJC"].

To solve this, we will follow these steps −

• Define array ret and a map called graph.

• Define a method called visit. This will take airport name as input

• while size of the graph[airport] is not 0

• x := first element of graph[airport]

• delete the first element from graph[airport]

• call visit(x)

• insert airport into ret

• Now from the main method, do the following −

• for i in range 0 to size of tickers array

• u := tickets[i, 0], v := tickets[i, 1], insert v into graph[u]

• visit(“KLK”) as this is the first airport

• reverse the list ret and return

Let us see the following implementation to get better understanding −

## Example

#include <bits/stdc++.h>
using name space std;
void print_vector(vector<auto> v){
cout < "[";
for(int i = 0; i<v.size(); i++){
cout << v[i] << ", ";
}
cout << "]"<<endl;
}
class Solution {
public:
vector <string> ret;
map < string, multiset <string> > graph;
vector<string> findItinerary(vector<vector<string>>& tickets) {
for(int i = 0; i < tickets.size(); i++){
string u = tickets[i][0];
string v = tickets[i][1];
graph[u].insert(v);
}
visit("KLK");
reverse(ret.begin(), ret.end());
return ret;
}
void visit(string airport){
while(graph[airport].size()){
string x = *(graph[airport].begin());
graph[airport].erase(graph[airport].begin());
visit(x);
}
ret.push_back(airport);
}
};
main(){
Solution ob;
vector<vector<string>> v ={{"MUC","LHR"},{"KLK","MUC"},{"SFO","SJC"},{"LHR","SFO"}};
print_vector(ob.findItinerary(v));
}

## Input

{{"MUC","LHR"},{"KLK","MUC"},{"SFO","SJC"},{"LHR","SFO"}}

## Output

[KLK, MUC, LHR, SFO, SJC, ]

Updated on: 08-Oct-2020

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