[Algospot]Dictionary - Topological Sort[graph - DFS]

https://algospot.com/judge/problem/read/DICTIONARY#

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
 
using namespace std;
 
vector<string> words;
vector<vector<int> > adj;
vector<int> seen, order;
int C;
int N;
 
void makeGraph(const vector<string>& words){
 adj = vector<vector<int> >(26, vector<int>(26, 0));
 for(int j = 1; j < words.size(); ++j){
  int i = j-1;
  int len = min(words[i].size(), words[j].size());
 
  for(int k = 0; k < len; ++k){
   if(words[i][k] != words[j][k]){
    int a = words[i][k] - 'a';
    int b = words[j][k] - 'a';
    adj[a][b] = 1;
    break;
   }
  }
 }
}
 
void dfs(int here){
 seen[here] = 1;
 for(int there = 0; there < adj.size(); ++there)
  if(adj[here][there] && !seen[there])
   dfs(there);
 order.push_back(here);
}
 
vector<int> topologicalSort(){
 int n = adj.size();
 seen = vector<int>(n, 0);
 order.clear();
 for(int i = 0; i < n; ++i)
  if(!seen[i])
   dfs(i);
 reverse(order.begin(), order.end());
 
 for(int i = 0; i < n; ++i)
  for(int j = i + 1; j < n; ++j)
   if(adj[order[j]][order[i]])
    return vector<int>();
 
 return order;
}
 
int main(){
 cin >> C;
 
 for(int j = 0; j < C; j++){
  cin >> N;
  words.clear();
  for(int i = 0; i < N; i++){
   string temp;
   cin >> temp;
   words.push_back(temp);
  }
 
  makeGraph(words);
  
  vector<int> arr = topologicalSort();
  
  /*for(int j = 0; j < adj.size(); j++){
   for(int i = 0; i < adj.size(); i++){
    cout << adj[j][i] << " ";  
   }
   cout << endl;
  }*/
  
  if(arr.empty()) cout << "INVALID HYPOTHESIS" << endl;
 
  else{
   for(int i = 0; i < arr.size(); i++){
    //cout << arr[i] << " ";
    char temp;
    temp = (char)(arr[i] + 'a');
    cout << temp;
   }
   cout << endl;
  }
 }
 return 0;
}