How to find subsequences of a given vector, excluding given positions?

Question

Given the vector v:

[7 , 8 , 30 , -2 , 9]  

And the vector rem, which contains, in ascending order, the positions removed:

[1 , 4]

It is necessary to do a function seq(rem,n) (where n is the number of vector elements) that will return the beginning and end of each of the subsequences that does not contain the removed positions:

[(0,0) , (2,3)]

I tried to start with some special cases:

if(len(r) == 0):
    return [(0,n-1)]
elif(len(r) == 1):
    if(r[0] == 0):
      return [(1,n-1)]
    elif(r[0] == n -1):
      return [(0, n-2)]
    else:
      return [(0, r[0]-1), (r[0]+1, n-1)]

Then the general cases:

sequencias = []
if(r[0] == 0):
    if(r[1] != 1):
      sequencias.append((1, r[1]-1))
    elif(r[1] == 1 and len(r) ==2):
      sequencias.append((r[1]+1 , n-1))
      return sequencias
else:
    if(r[1] - r[0] > 1):
      sequencias.append((r[0]+1 , r[1]-1))

  
for i in range(1,len(r)-1):
    if(r[i+1] - r[i]  > 1):
      sequencias.append((r[i]+1 , r[i+1]-1))


  return sequencias