Longest Consecutive Sequence
Given an array of integers nums, return the length of the longest consecutive sequence of elements that can be formed.

A consecutive sequence is a sequence of elements in which each element is exactly 1 greater than the previous element. The elements do not have to be consecutive in the original array.

You must write an algorithm that runs in O(n) time.

Example 1:

Input: nums = [2,20,4,10,3,4,5]

Output: 4
Explanation: The longest consecutive sequence is [2, 3, 4, 5].

Example 2:

Input: nums = [0,3,2,5,4,6,1,1]

Output: 7
Constraints:

0 <= nums.length <= 1000
-10^9 <= nums[i] <= 10^9

# Solution

[2,20,4,10,3,4,5]

# 1
e = 2
[[2]]

# 2 
e = 20
[[2], [20]]

# 3
e = 4
[[2], [20], [4]]

# 4
e = 10
[[2], [20], [4], [10]]

# 5 
e = 3
[[2,3], [20], [4], [10]]

# 6
e = 4
[[2,3,4], [20], [4], [10]]

# 7
e = 5
[[2,3,4,5], [20], [4], [10]]