const STACK_SIZE: usize = 128 * 1024 * 1024;

fn run() {
    //...
}

fn main() {
    let child = std::thread::Builder::new()
        .stack_size(STACK_SIZE)
        .spawn(run)
        .unwrap();
    child.join().unwrap();
}

This text helped me:)
1 2
1 4
1 3
2 4
2 3
3 4
3 5
5 6
5 8
8 7
7 6
6 8

Check if your solution works correctly with dense graphs

This problem is easier than rating should be if you know the trick.

Invariant: graph G is decomposable if and only if all the connected components of G has even number of edges.

A tree is very easy to be decomposed. Creating a tree equivalent to each connected component will lead to the answer.

Hope this help, Mick :)

1 2
2 3
2 4
2 5

1 2
2 3
1 3
3 4
4 5
4 1
1 5
2 5