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.

The step-through player is coming for this one. Two Sum has the full animation today; the rest are being authored in the admin.

Pythontime O(n) · space O(n)

def longestConsecutive(nums: list[int]) -> int:
    num_set = set(nums)
    best = 0
    for n in num_set:
        if n - 1 not in num_set:  # start of a sequence
            cur = n
            while cur in num_set:
                cur += 1
            best = max(best, cur - n)
    return best

Next upValid Palindrome

Two Sum is free. Enroll to unlock every visualization and save where you stopped.Enroll free

Watch the video walkthrough