Hackerland radio transmitters

1def hackerlandRadioTransmitters(arr, k, n):
2  arr.sort()
3  i, res, last = 0, 0, -math.inf
4  
5  while i < n:
6    if arr[i] <= last + k: 
7      i += 1
8      continue
9    
10    j = i
11    while j < n and arr[i] >= arr[j] - k: j += 1
12    
13    res += 1
14    last = arr[j - 1]
15    
16    if i == j: i += 1
17    else: i = j
18  
19  return res