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import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;
import java.util.stream.IntStream;
public class StronglyConnected {
private static int numberOfStronglyConnectedComponents(ArrayList<Integer>[] adj) {
ArrayList<Integer>[] adjReversa1 = reverseG(adj);
boolean[] adjReversalVisited = new boolean[adj.length];
int[] postV = new int[adj.length];
int[] clock = new int[1];
dfs(adjReversa1, adjReversalVisited, postV, clock);
// https://stackoverflow.com/questions/951848/java-array-sort-quick-way-to-get-a-sorted-list-of-indices-of-an-array/35701049
int[] temp = IntStream.range(0, postV.length).boxed().sorted((i, j) -> postV[i] - postV[j]).mapToInt(ele -> ele).toArray();
boolean[] visited = new boolean[adj.length];
int sccCount = 0;
for (int i = adj.length - 1; i > -1; i--) {
if (!visited[temp[i]]) {
exploreWithoutPostV(temp[i], adj, visited);
sccCount++;
}
}
return sccCount;
}
private static void dfs(ArrayList<Integer>[] adj, boolean[] visited, int[] postV, int[] clock) {
for (int v = 0; v < adj.length; v++) {
if (!visited[v])
explore(v, adj, visited, postV, clock);
}
}
private static void explore(int v, ArrayList<Integer>[] adj, boolean[] visited, int[] postV, 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;
}
private static void exploreWithoutPostV(int v, ArrayList<Integer>[] adj, boolean[] visited) {
visited[v] = true;
for (int w : adj[v]) {
if (!visited[w])
exploreWithoutPostV(w, adj, visited );
}
}
private static ArrayList<Integer>[] reverseG(ArrayList<Integer>[] adj) {
ArrayList<Integer>[] adjReverse = (ArrayList<Integer>[])new ArrayList[adj.length];
for (int i = 0; i < adj.length; i++) {
adjReverse[i] = new ArrayList<Integer>();
}
for (int v = 0; v < adj.length; v++) {
for (int w : adj[v]) {
adjReverse[w].add(v);
}
}
return adjReverse;
}
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int n = scanner.nextInt();
int m = scanner.nextInt();
ArrayList<Integer>[] adj = (ArrayList<Integer>[])new ArrayList[n];
for (int i = 0; i < n; i++) {
adj[i] = new ArrayList<Integer>();
}
for (int i = 0; i < m; i++) {
int x, y;
x = scanner.nextInt();
y = scanner.nextInt();
adj[x - 1].add(y - 1);
}
System.out.println(numberOfStronglyConnectedComponents(adj));
}
}
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