Given an unsorted array of integers, find the length of the longest consecutive elements sequence. Well, lets assume that this task related only to the sequence with step equal to 1 only.
Given exampleArray = [100, 4, 200, 1, 3, 2]
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The longest consecutive elements sequence is [1, 2, 3, 4]
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longestConsecutiveLength(exampleArray)
returns the length of the longest sequence - 4
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Your algorithm should have O(n) complexity.