250319 단절선

static class Node implements Comparable<Node> {
	int from, to;

	Node(int from, int to) {
		this.from = from;
		this.to = to;
	}

	@Override
	public int compareTo(Node o) {
		return this.from != o.from ? this.from - o.from : this.to - o.to;
	}
}

public static void main(String[] args) throws Exception {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	StringTokenizer st = new StringTokenizer(br.readLine());
	int v = Integer.parseInt(st.nextToken());
	int e = Integer.parseInt(st.nextToken());

	List<List<Integer>> graph = createGraph(v, e, br);
	List<Node> bridges = findBridges(v, graph);

	StringBuilder sb = new StringBuilder();
	sb.append(bridges.size()).append('\n');
	for (Node bridge : bridges) {
		sb.append(bridge.from).append(' ').append(bridge.to).append('\n');
	}
	System.out.print(sb);
}

private static List<List<Integer>> createGraph(int v, int e, BufferedReader br) throws IOException {
	List<List<Integer>> graph = new ArrayList<>();
	for (int i = 0; i <= v; i++) {
		graph.add(new ArrayList<>());
	}

	while (e-- > 0) {
		StringTokenizer st = new StringTokenizer(br.readLine());
		int a = Integer.parseInt(st.nextToken());
		int b = Integer.parseInt(st.nextToken());
		graph.get(a).add(b);
		graph.get(b).add(a);
	}
	return graph;
}

private static List<Node> findBridges(int v, List<List<Integer>> graph) {
	int[] visit = new int[v + 1];
	int[] order = { 1 };
	List<Node> bridges = new ArrayList<>();

	for (int i = 1; i <= v; i++) {
		if (visit[i] == 0) {
			dfs(i, 0, graph, visit, order, bridges);
		}
	}

	bridges.sort(Comparator.naturalOrder());
	return bridges;
}

private static int dfs(int cur, int parent, List<List<Integer>> graph, int[] visit, int[] order,
		List<Node> bridges) {
	visit[cur] = order[0]++;
	int result = visit[cur];

	for (int next : graph.get(cur)) {
		if (next == parent)
			continue;

		if (visit[next] > 0) {
			result = Math.min(result, visit[next]);
			continue;
		}

		int prev = dfs(next, cur, graph, visit, order, bridges);
		if (prev > visit[cur]) {
			bridges.add(new Node(Math.min(cur, next), Math.max(cur, next)));
		}
		result = Math.min(result, prev);
	}
	return result;
}

출처:https://www.acmicpc.net/problem/11400