bfs

public void traverse(int[][] G, int start){
    int[] visited = new int[G.length];
    Queue<Integer> queue = new LinkedList<>();

    System.out.print(start + " ");
    // visited first 1 node
    visited[start] = 1;
    // insert into the queue
    queue.add(start);

    while (!queue.isEmpty()){
        int u = queue.remove();
        for (int v = 1; v < G.length; v++){
            if(G[u][v] == 1 && visited[v] == 0){
                System.out.print(v + " ");
                visited[v] = 1;
                queue.add(v);
            }
        }
    }
}