level_2/30.rs

use vstd::prelude::*;
fn main() {}
verus!{



fn f1_max_length_list(seq: &Vec<Vec<i32>>) -> (max_list: &Vec<i32>)
    requires
        seq.len() > 0,
{
    let mut max_list = &seq[0];
    let mut index = 1;

    while index < seq.len()
    {
        if ((seq[index]).len() > max_list.len()) {
            max_list = &seq[index];
        }
        index += 1;
    }
    max_list
}





fn f2_find_negative_numbers(arr: &Vec<i32>) -> (negative_list: Vec<i32>)
{
    let mut negative_list: Vec<i32> = Vec::new();
    let input_len = arr.len();

    let mut index = 0;
    while index < arr.len()
    {
        if (arr[index] < 0) {
            negative_list.push(arr[index]);
        }
        index += 1;
    }
    negative_list
}



spec fn step1(__hp0: Seq<Vec<i32>>, outp: Seq<i32>) -> bool {
    (forall|k: int| 0 <= k < __hp0.len() ==> outp.len() >= #[trigger] (__hp0[k]).len())
    && (exists|k: int| 0 <= k < __hp0.len() && outp =~= #[trigger] (__hp0[k]@))
}

spec fn step2(inp: Seq<i32>, outp: Seq<i32>) -> bool {
    (outp == inp.filter(|x: i32| x < 0))
}

fn chain_driver(seq: &Vec<Vec<i32>>) -> (r_final: Vec<i32>)
    requires
        seq.len() > 0,
    ensures
        exists|v1: Seq<i32>| #[trigger] step1(seq@, v1) && step2(v1, r_final@),
{
    let x1 = f1_max_length_list(seq);
    let x2 = f2_find_negative_numbers(x1);
    proof {
        assert(step1(seq@, x1@));
        assert(step2(x1@, x2@));
    }
    x2
}

} // verus!