[LeetCode] Problem 133 - Clone Graph

Given a reference of a node in a connected undirected graph, return a deep copy (clone) of the graph. Each node in the graph contains a val (int) and a list (List[Node]) of its neighbors.

Example

Input:
{“$id”:”1”,”neighbors”:[{“$id”:”2”,”neighbors”:[{“$ref”:”1”},{“$id”:”3”,”neighbors”:[{“$ref”:”2”},{“$id”:”4”,”neighbors”:[{“$ref”:”3”},{“$ref”:”1”}],”val”:4}],”val”:3}],”val”:2},{“$ref”:”4”}],”val”:1}

Explanation:
Node 1’s value is 1, and it has two neighbors: Node 2 and 4.
Node 2’s value is 2, and it has two neighbors: Node 1 and 3.
Node 3’s value is 3, and it has two neighbors: Node 2 and 4.
Node 4’s value is 4, and it has two neighbors: Node 1 and 3.

Note

The number of nodes will be between 1 and 100.

The undirected graph is a simple graph, which means no repeated edges and no self-loops in the graph.

Since the graph is undirected, if node p has node q as neighbor, then node q must have node p as neighbor too.

You must return the copy of the given node as a reference to the cloned graph.

O(n) runtime, O(n) space – Depth-first traversal

public class UndirectedGraphNode {
    int label;
    List<UndirectedGraphNode> neighbors;
    UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
}

public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
    if (node == null)
        return null;

    Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
    return dfs(map, node);
}

private UndirectedGraphNode dfs(Map<UndirectedGraphNode, UndirectedGraphNode> map, UndirectedGraphNode node) {
    UndirectedGraphNode copy = new UndirectedGraphNode(node.label);
    map.put(node, copy);

    for (UndirectedGraphNode neighbor : node.neighbors) {
        if (!map.containsKey(neighbor))
            copy.neighbors.add(dfs(map, neighbor));
        else
            copy.neighbors.add(map.get(neighbor));
    }

    return copy;
}

O(n) runtime, O(n) space – Breadth-first traversal

public class UndirectedGraphNode {
    int label;
    List<UndirectedGraphNode> neighbors;
    UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
}

public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
    if (node == null)
        return null;

    Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
    return bfs(map, node);
}

private UndirectedGraphNode bfs(Map<UndirectedGraphNode, UndirectedGraphNode> map, UndirectedGraphNode node) {
    Queue<UndirectedGraphNode> queue = new LinkedList<>();
    UndirectedGraphNode copy = new UndirectedGraphNode(node.label);
    map.put(node, copy);
    queue.offer(node);

    while (!queue.isEmpty()) {
        UndirectedGraphNode current = queue.poll();

        for (UndirectedGraphNode neighbor : current.neighbors) {
            if (!map.containsKey(neighbor)) {
                queue.offer(neighbor);
                map.put(neighbor, new UndirectedGraphNode(neighbor.label));
            }

            map.get(current).neighbors.add(map.get(neighbor));
        }
    }

    return copy;
}