day 16 phase calculator

phase.rs

fn next_phase(nums: &[i64], strt: usize) -> Vec<i64> {
    let mut pfs = vec![0];
    pfs.extend(nums);
    for i in 1..pfs.len() {
        pfs[i] += pfs[i-1];
    }

    let mut newl = Vec::with_capacity(nums.len());

    for n in strt..nums.len()+strt {

        let mut newn = 0;

        let mut j = n;
        while j < nums.len()+strt {
            newn += pfs[(j+n-strt+1).min(pfs.len()-1)] - pfs[j-strt];
            j += 4*(n+1);
        }

        let mut j = 2*(n+1)+n;
        while j < nums.len()+strt {
            newn -= pfs[(j+n-strt+1).min(pfs.len()-1)] - pfs[j-strt];
            j += 4*(n+1);
        }

        newl.push(newn.abs() % 10);
    }
    newl
}