250608 Boomerangs

@SuppressWarnings("unchecked")
public static void main(String[] args) throws IOException {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

	int[] nm = parseInput(br);
	int nodes = nm[0], edges = nm[1];

	List<Integer>[] graph = new ArrayList[nodes + 1];
	List<Integer>[] children = new ArrayList[nodes + 1];
	for (int i = 0; i <= nodes; i++) {
		graph[i] = new ArrayList<>();
		children[i] = new ArrayList<>();
	}

	for (int i = 0; i < edges; i++) {
		int[] edge = parseInput(br);
		int node1 = edge[0], node2 = edge[1];
		graph[node1].add(node2);
		graph[node2].add(node1);
	}

	boolean[] visited = new boolean[nodes + 1];
	int[] parent = new int[nodes + 1];
	int[] childCount = new int[nodes + 1];
	List<int[]> triplets = new ArrayList<>();
	int[] components = new int[1];

	for (int i = 1; i <= nodes; i++) {
		if (!visited[i]) {
			dfs(i, graph, children, visited, parent, childCount, triplets, components);
		}
	}

	bw.write(Integer.toString(components[0]));
	bw.newLine();
	for (int[] triplet : triplets) {
		bw.write(triplet[0] + " " + triplet[1] + " " + triplet[2]);
		bw.newLine();
	}
	bw.flush();
	bw.close();
}

private static void dfs(int node, List<Integer>[] graph, List<Integer>[] children, boolean[] visited,
		int[] parent, int[] childCount, List<int[]> triplets, int[] components) {
	visited[node] = true;
	childCount[node] = graph[node].size();

	for (int neighbor : graph[node]) {
		if (visited[neighbor]) {
			if (parent[node] != neighbor) {
				children[neighbor].add(node);
			}
			childCount[neighbor]--;
		} else {
			parent[neighbor] = node;
			dfs(neighbor, graph, children, visited, parent, childCount, triplets, components);
		}
	}

	components[0] += childCount[node] / 2;

	if (childCount[node] % 2 == 1 && parent[node] != 0) {
		childCount[parent[node]]++;
	}

	List<Integer> childList = children[node];
	int size = childList.size();
	for (int i = 1; i < size; i += 2) {
		triplets.add(new int[] { childList.get(i - 1), node, childList.get(i) });
	}

	if (size % 2 == 1 && parent[node] != 0) {
		triplets.add(new int[] { childList.get(size - 1), node, parent[node] });
	} else if (size % 2 == 0 && parent[node] != 0) {
		children[parent[node]].add(node);
	}
}

private static int[] parseInput(BufferedReader br) throws IOException {
	String[] parts = br.readLine().split(" ");
	int[] result = new int[parts.length];
	for (int i = 0; i < parts.length; i++) {
		result[i] = Integer.parseInt(parts[i]);
	}
	return result;
}

출처:https://www.acmicpc.net/problem/16583