#+ANKI_DECK: study_deck_02
* TODO 0128. Longest Consecutive Sequence :medium:
:PROPERTIES:
:NEETCODE: [[file:../../roadmap.org::*0128. Longest Consecutive Sequence][0128. Longest Consecutive Sequence]]
:END:

Given an unsorted array of integers ~nums~, return /the length of the longest consecutive elements sequence./

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

*Example 1:*


#+begin_src
Input: nums = [100,4,200,1,3,2]
Output: 4
Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.
#+end_src


*Example 2:*


#+begin_src
Input: nums = [0,3,7,2,5,8,4,6,0,1]
Output: 9
#+end_src


*Example 3:*


#+begin_src
Input: nums = [1,0,1,2]
Output: 3
#+end_src


*Constraints:*

 - ~0 <= nums.length <= 10^{5}~

 - ~-10^{9} <= nums[i] <= 10^{9}~

** TODO Approach
Write your approach here.

** TODO Python
#+begin_src python
class Solution:
    def longestConsecutive(self, nums: List[int]) -> int:
#+end_src

** TODO C++
#+begin_src cpp
class Solution {
public:
    int longestConsecutive(vector<int>& nums) {
        
    }
};
#+end_src