Hi, here's your problem today. This problem was recently asked by Amazon:

You are given an array of integers. Return the length of the longest consecutive elements sequence in the array.

For example, the input array [100, 4, 200, 1, 3, 2] has the longest consecutive sequence 1, 2, 3, 4, and thus, you should return its length, 4.

<pre lang=py>
def longest_consecutive(nums):
  # Fill this in.

print longest_consecutive([100, 4, 200, 1, 3, 2])
# 4
</pre>

Can you do this in linear time?