def METHOD_NAME(graph):
    """Returns the nodes in a graph that do not have inputs.
    Notes
    -----
    The graph must be directed and acyclic.
    Parameters
    ----------
    graph: dict(str, list(str))
        The graph to explore. Each key in the dictionary represents a node in the graph, and each
        string in the value list represents a node which depends on the node defined by the key.
    Returns
    -------
    list(str)
        The root nodes of the graph.
    """
    dependencies = dependants_to_dependencies(graph)
    root_nodes = []
    for node_key in dependencies:
        if len(dependencies[node_key]) > 0:
            continue
        root_nodes.append(node_key)
    return root_nodes