Function sfcpl::inversation::inversation

pub fn inversation(v: &Vec<usize>) -> usize

配列の転倒数をFenwickTreeを利用してカウント

O(n log n)

#test fn inversation_test() { let v = vec![3, 1, 2]; assert_eq!(inversation(&v), 2); let v = vec![3, 2, 1]; assert_eq!(inversation(&v), 3); let v = vec![3, 3, 3]; assert_eq!(inversation(&v), 0); let v = vec![1, 2, 4, 3, 6, 5]; assert_eq!(inversation(&v), 2); }