Next element in arithmetic sequence

Problem to find next arithmetic sequence in given sequence.

Example-1:

Input    : n = [ 1, 3, 5, 7]
Output   : 9  

Example-2:

Input    : n = [ 10, 8, 6]
Output   : 4 

Solution

n = [ 1, 3, 5, 7]

a = n[-1] + (n[-1]-n[-2])

print(a)

Output

9