fn f(v : &[&[u32]], cur: &mut Vec<u32>, r : &mut Vec<Vec<u32>>){
    if v.is_empty() {
        r.push(cur.clone());
        return;
    }

    let first = v[0];
    let others = &v[1..];
    for &x in first.iter() {
        cur.push(x);
        f(others,cur,r);
        cur.pop();
    }
}

fn g(v : &[&[u32]]) -> Vec<Vec<u32>> {
    let mut cur = vec![];
    let mut ret = vec![];
    f(v,&mut cur, &mut ret);
    ret
}

fn main() {
    let v = [&[1,2,3,4][..],&[5,6,7,8][..]];

    println!("FIRST {:#?}",g(&v));

    let v = [&[1,2,3,4][..],&[5,6,7,8][..],&[9,10,11,12][..]];

    println!("SECOND {:#?}",g(&v));

    let v = [&[1,2,3,4][..],&[5,6,7,8][..],&[9,10,11,12][..],&[13,14,15,16][..]];

    println!("THIRD {:#?}",g(&v));
}