# 128. Longest Consecutive Sequence Leetcode Solution

## Longest Consecutive Sequence Leetcode Problem :

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.

## Longest Consecutive Sequence Leetcode Solution :

### Constraints :

• 0 <= nums.length <= 105
• -109 <= nums[i] <= 109

### Example 1:

• Input: nums = [0,3,7,2,5,8,4,6,0,1]
• Output: 9

Approach :

1. insert all the nums elements in a set, now the set will contain all the unique elements in the array.
2. now traverse the array nums.
3. if there is any smaller elemets in the set from num[i], then continue because for the longest sequence we will have to start
from the smallest element of the given sequence.
4. if there is no any smaller element than nums[i] in the set, then starting from current element maitain a while loop until the next element is not present in the set. Now update the ans variable.
5. finally we get the answer.

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