How to implement a breadth first search to a certain depth?

Question

I understand and can easily implement BFS.

My question is, how can we make this BFS limited to a certain depth? Suppose, I just need to go 10 level deep.

Answer 1

This works. Assuming that visited flag is not there in Node. If isVisited is available, then there no need to tracker Map.

// k is depth, result should not contain initialNode.
public static Collection bfsWithK_Depth(Node initialNode, int k) {

    if (initialNode == null || k <= 0) {
        return new ArrayList<>();
    }

    Queue q = new LinkedList<>();
    q.add(initialNode);
    Map tracker = new HashMap(); // no need if there is visited flag.
    Collection result = new ArrayList<>();

    while (!q.isEmpty()) { // Q will be filled only with eligible nodes
        --k ;
        Node node = q.remove();
        List neighbor = node.getNeighbor();
        for (Node n : neighbor) {
            if (tracker.get(n) == null && k > 0) {
                q.add(n);
            }
            if (tracker.get(n) == null) { 
                tracker.put(n, n); 
                result.add(n); // visit this node
            }
        }

    }
    return result;
}