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, ]