import torch
import numpy as np


def dfill(a):
    n = torch.numel(a)
    b = torch.cat([
        torch.tensor([0]),
        torch.nonzero(a[:-1] != a[1:], as_tuple=True)[0] + 1,
        torch.tensor([n])
    ])
    # print('b:',b)
    res = torch.arange(n)[b[:-1]]
    res = torch.repeat_interleave(res, b[1:] - b[:-1])
    return res


def argunsort(s):
    n = torch.numel(s)
    u = torch.empty(n, dtype=torch.int64)
    u[s] = torch.arange(n)
    return u


def cumcount(a):
    n = torch.numel(a)
    s = np.argsort(a.detach().cpu().numpy(), kind='mergesort')
    s = torch.tensor(s, device=a.device)
    i = argunsort(s)
    b = a[s]
    return (torch.arange(n) - dfill(b))[i]