Hi, here’s your problem today. This problem was recently asked by Facebook:

Given a sequence of numbers, find the longest sequence that contains only 2 unique numbers.

Example:

Input: [1, 3, 5, 3, 1, 3, 1, 5]
Output: 4

The longest sequence that contains just 2 unique numbers is [3, 1, 3, 1]

Here’s the solution signature:

def findSequence(seq):
  # Fill this in.

print findSequence([1, 3, 5, 3, 1, 3, 1, 5])
# 4