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//#include <gtest/gtest.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <numeric>
using std::vector;
using std::pair;
using namespace std;
// https://stackoverflow.com/questions/1577475/c-sorting-and-keeping-track-of-indexes
template<typename T>
vector<size_t> sort_indexes(const vector<T> &v) {
// initialize original index locations
vector<size_t> idx(v.size());
iota(idx.begin(), idx.end(), 0);
// sort indexes based on comparing values in v
// using std::stable_sort instead of std::sort
// to avoid unnecessary index re-orderings
// when v contains elements of equal values
stable_sort(idx.begin(), idx.end(), [&v](size_t i1, size_t i2) {
return v[i1] > v[i2];
});
return idx;
}
void exploreWithoutPostV(int v, vector<vector<int>> &adj,
vector<bool> &visited) {
visited[v] = true;
for (int w : adj[v]) {
if (!visited[w])
exploreWithoutPostV(w, adj, visited);
}
}
void explore(int v, vector<vector<int>> &adj, vector<bool> &visited,
vector<int> &postV, vector<int> &clock) {
visited[v] = true;
for (int w : adj[v]) {
if (!visited[w])
explore(w, adj, visited, postV, clock);
}
postV[v] = clock[0];
clock[0] = clock[0] + 1;
}
void dfs(vector<vector<int> > &adj, vector<bool> &visited, vector<int> &postV,
vector<int> &clock) {
for (size_t v = 0; v < adj.size(); v++) {
if (!visited[v])
explore(v, adj, visited, postV, clock);
}
}
vector<vector<int>> reverseG(vector<vector<int>> &adj) {
vector<vector<int> > adjReverse(adj.size(), vector<int>());
for (size_t v = 0; v < adj.size(); v++) {
for (int w : adj[v]) {
adjReverse[w].push_back(v);
}
}
return adjReverse;
}
int number_of_strongly_connected_components(vector<vector<int> > adj) {
int result = 0;
vector<vector<int>> adjReversal = reverseG(adj);
vector<bool> adjReversalVisited(adj.size(), false);
vector<int> postV(adj.size(), 0);
vector<int> clock(1, 0);
dfs(adjReversal, adjReversalVisited, postV, clock);
vector<bool> visited(adj.size(), false);
for (auto i : sort_indexes(postV)) {
if (!visited[i]) {
exploreWithoutPostV(i, adj, visited);
result++;
}
}
//write your code here
return result;
}
int main() {
size_t n, m;
std::cin >> n >> m;
vector<vector<int> > adj(n, vector<int>());
for (size_t i = 0; i < m; i++) {
int x, y;
std::cin >> x >> y;
adj[x - 1].push_back(y - 1);
}
std::cout << number_of_strongly_connected_components(adj);
}
//TEST(Acyclicity, ac1) {
// vector<vector<int>> adj = { { 1 }, { 2 }, { 0 }, { 0 } };
// ASSERT_EQ(acyclic(adj), 1);
//}
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