백준 11724번: 연결 요소의 개수

public static void main(String[] args) throws IOException {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

    int[] nm = convertStringArrayToIntegerArray(br.readLine().split(" "));
    int n = nm[0];
    int m = nm[1];

    boolean[][] graph = new boolean[n+1][n+1];
    while (m-- > 0) {
        int[] xy = convertStringArrayToIntegerArray(br.readLine().split(" "));

        graph[xy[0]][xy[1]] = true;
        graph[xy[1]][xy[0]] = true;
    }

    int answer = 0;

    boolean[] isVisit = new boolean[n+1];
    for (int i = 1; i < graph.length; i++) {
        if (!isVisit[i]) {
            answer += bfs(isVisit, graph, i);
        }
    }

    System.out.println(answer);
}

private static int[] convertStringArrayToIntegerArray(String[] args) {
    int[] array = new int[args.length];
    int i = 0;
    for (String str : args) {
        array[i++] = Integer.parseInt(str);
    }

    return array;
}

private static int bfs(boolean[] isVisit, boolean[][] graph,int startIndex) {
    Queue<Integer> queue = new LinkedList<>();
    queue.offer(startIndex);
    isVisit[startIndex] = true;

    while (!queue.isEmpty()) {
        int x = queue.poll();

        for (int i = 1; i < isVisit.length; i++) {
            if (isVisit[i]) {
                continue;
            }

            if (graph[x][i]) {
                queue.offer(i);
                isVisit[i] = true;
            }
        }
    }

    return 1;
}