Factory

//package hiit;

import java.util.*;

public class F {
	
	static HashSet<Integer>[] downLine;
	static int[] children;
	static int[] parents;
	static PriorityQueue<Job> q;

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		int m = scanner.nextInt();
		children = new int[n+1];
		parents = new int[n+1];
		downLine = new HashSet[n+1];
		for (int i=1; i<=n; i++) {
			downLine[i] = new HashSet();
		}
		for (int i=1; i<=m; i++) {
			int a = scanner.nextInt();
			int b = scanner.nextInt();
			downLine[a].add(b);
			children[a]++;
			parents[b]++;
		}
		
		q = new PriorityQueue<>();
		for (int i=1; i<=n; i++) {
			if (parents[i] == 0) {
				q.add(new Job(i, children[i]));
			}
		}
		
		int time = 0;
		while (!q.isEmpty()) {
			time++;
			Job wait = q.poll();
			if (!q.isEmpty()) work(q.poll());
			work(wait);
		}
		
		System.out.println(time);
	}
	
	static void work(Job job) {
		for (Integer child : downLine[job.node]) {
			parents[child]--;
			if (parents[child] == 0) {
				q.add(new Job(child, children[child]));
			}
		}
	}
	
	

}

class Job implements Comparable<Job> {
	int node;
	int children;
	
	public Job(int node, int children) {
		this.node = node;
		this.children = children;
	}

	@Override
	public int compareTo(Job o) {
		if (this.children > o.children) return -1;
		if (this.children < o.children) return 1;
		return 0;
	}
	
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: ACCEPTED

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: WRONG ANSWER

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: ACCEPTED

Test 12

Verdict: WRONG ANSWER

Test 13

Verdict: ACCEPTED

Test 14

Verdict: WRONG ANSWER

Test 15

Verdict: ACCEPTED

Test 16

Verdict: WRONG ANSWER

Test 17

Verdict: WRONG ANSWER