nicopappl

    struct JaggedArray<T> {
        offsets: Vec<u32>,
        data: Vec<T>,
    }
    // impl JaggedArray<T>
    fn add_row(&mut self, row: Vec<T>) {
        self.data.extend(row);
        self.offsets.push(self.len());
    }
    fn get_row(&self, row: usize) -> &[T] {
        let start = self.offsets[row] as usize;
        let end =  self.offsets[row + 1] as usize;
        &self.data[start..end]
    }

    fn get_row(&self, row: usize) -> &[T] {
        let start = if row == 0 { 0 } else { self.offsets[row - 1] as usize };
        let end =  self.offsets[row] as usize;
        &self.data[start..end]
    }