638B - Making Genome in Berland - CodeForces Solution

#include<bits/stdc++.h>

using namespace std;

int n, cha[35];

string s;

set <int> graph[30];

bool visited[35];

bool tontai[35];

int timcha(int u){
    if(u == cha[u]) return u;
    return timcha(cha[u]);
}

void dfs(int u, int p){
    cout << char('a' + u);
    visited[u] = true;
    for(auto x : graph[u]) dfs(x, u);
}

int main(){
    ios_base :: sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin >> n;
    for(int i = 0; i <= 30; i++) cha[i] = i;
    for(int i = 1; i <= n; i++){
        cin >> s;
        tontai[s[0] - 'a'] = true;
        for(int i = 1; i < s.size(); i++){
            tontai[s[i] - 'a'] = true;
            cha[s[i] - 'a'] = s[i - 1] - 'a';
            graph[s[i - 1] - 'a'].insert(s[i] - 'a');
        }
    }
    for(int i = 0; i < 26; i++){
        if(!visited[i] && tontai[i]) dfs(timcha(i), 0);
    }
    return 0;
}