[Solved] 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.

Question

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:

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.

Example 2:

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

Constraints:

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

Python Solution

from heapq import heappush,heappop,heapify

class Solution:
    def longestConsecutive(self, nums: List[int]) -> int:
        nums = list(set(nums))
        heapify(nums)
        prev = -float('inf')
        r = 1
        m = 0
        i = len(nums)-1
        
        while i!=-1:
            curr = heappop(nums)
            if prev+1==curr:
                r+=1
            else:
                r = 1
            
            m = max(m,r)
            prev = curr
            i-=1
        
        return m