## C++, graph, topological_sort.cpp

``````#include <algorithm>
#include <iostream>
#include <vector>

int number_of_vertices,
number_of_edges;  // For number of Vertices (V) and number of edges (E)
std::vector<std::vector<int>> graph;
std::vector<bool> visited;
std::vector<int> topological_order;

void dfs(int v) {
visited[v] = true;
for (int u : graph[v]) {
if (!visited[u]) {
dfs(u);
}
}
topological_order.push_back(v);
}

void topological_sort() {
visited.assign(number_of_vertices, false);
topological_order.clear();
for (int i = 0; i < number_of_vertices; ++i) {
if (!visited[i]) {
dfs(i);
}
}
reverse(topological_order.begin(), topological_order.end());
}
int main() {
std::cout
<< "Enter the number of vertices and the number of directed edges\n";
std::cin >> number_of_vertices >> number_of_edges;
int x = 0, y = 0;
graph.resize(number_of_vertices, std::vector<int>());
for (int i = 0; i < number_of_edges; ++i) {
std::cin >> x >> y;
x--, y--;  // to convert 1-indexed to 0-indexed
graph[x].push_back(y);
}
topological_sort();
std::cout << "Topological Order : \n";
for (int v : topological_order) {
std::cout << v + 1
<< ' ';  // converting zero based indexing back to one based.
}
std::cout << '\n';
return 0;
}
``````