DFS that calculates the b(u) and N(u) lookups, and also reorders the adjacency lists.

def __branch_point_dfs(dfs_data):
    """DFS that calculates the b(u) and N(u) lookups, and also reorders the adjacency lists."""
    u = dfs_data['ordering'][0]
    large_n = {}
    large_n[u] = 0
    stem = {}
    stem[u] = u
    b = {}
    b[u] = 1
    __branch_point_dfs_recursive(u, large_n, b, stem, dfs_data)
    dfs_data['N_u_lookup'] = large_n
    dfs_data['b_u_lookup'] = b
    return