[Link] https://AtCoder.jp/contests/typical90/tasks/typical90_u
Using class would make code lot more readable and easy to understand but I wanted to solved it fast since it’s late.
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import java.util.*;
import java.io.*;
public class Main {
public static int[] parentArr;
public static boolean[] end;
public static int cnt = 1;
public static long ans = 0;
public static Stack<Integer> stack = new Stack<>();
public static ArrayList<ArrayList<Integer>> edge = new ArrayList<ArrayList<Integer>>();;
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String[] line = br.readLine().split(" ");
int n = atoi(line[0]), m = atoi(line[1]);
parentArr = new int[n + 1];
end = new boolean[n + 1];
for(int i = 0; i <= n; i++) edge.add(new ArrayList<Integer>());
for(int i = 0; i < m; i++) {
line = br.readLine().split(" ");
edge.get(atoi(line[0])).add(atoi(line[1]));
}
for(int i = 1; i <= n; i++) if(parentArr[i] == 0) dfs(i);
System.out.println(ans);
}
public static int dfs(int v) {
int parent, count = 0;
parentArr[v] = parent = cnt++;
stack.push(v);
for(int desV : edge.get(v)) {
if(parentArr[desV] == 0) parent = Math.min(parent, dfs(desV));
else if(!end[desV]) parent = Math.min(parent, parentArr[desV]);
}
if(parent == parentArr[v]) {
while(true) {
count++;
int pop = stack.pop();
end[pop] = true;
if(pop == v) break;
}
ans += count * (count - 1l)/2;
}
return parent;
}
public static int atoi(String s) { return Integer.parseInt(s); }
}