# Question

Formatted question description: https://leetcode.ca/all/128.html

128. Longest Consecutive Sequence

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

For example,
Given [100, 4, 200, 1, 3, 2],
The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.

Your algorithm should run in O(n) complexity.

@tag-array



# Algorithm

For every num existed in set, try to probe to right to see if following numbers are also in set, and record longest possible sequence.

Java