You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: graph_enumeration.rs
    path of file: ./repos/Rust/src/graph
    
    the code of the file until where you have to start completion: use std::collections::BTreeMap;

type Graph<Vertex> = BTreeMap<Vertex, Vec<Vertex>>;

/*
This function creates a graph with vertices numbered from 1 to n for any input
`Graph<V>`. The result is in the form of Vec<Vec<usize> to make implementing
other algorithms on the graph easier and help with performance.

We expect that all vertices, even the isolated ones, to hav
    
    fn integer_vertices() {
        let mut graph = Graph::new();
        add_edge(&mut graph, 1001, 1002);
        add_edge(&mut graph, 1002, 1003);
        add_edge(&mut graph, 1003, 1001);
        add_edge(&mut graph, 1004, 1002);
        let mut result = enumerate_graph(&graph);
        let expected = vec![vec![], vec![2, 3], vec![1, 3, 4], vec![1, 2], vec![2]];

        result.iter_mut().for_each(|v| v.sort_unstable());
        assert_eq!(result, expected);
    }