as usize祭り絶賛開催中

unsafe fn calc(a_index: isize, b_index: isize) -> isize {
　if a_index == a.len() as isize { return 0; };
　let mut res: isize = 0;
　for i in b_index..b.len() as isize {
　　if a[a_index as usize] == b[b_index as usize] {
　　　res = res.max(calc(a_index + 1, b_index + 1) + 1);
　　}
　}
　res
}