📘

Longest Consecutive Sequence

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.

Input:

100,4,200,1,3,2

Output:

Reasoning:

First, we store the input values in a set for O(1) lookup: {100, 4, 200, 1, 3, 2}
Then, we iterate over the set and check if the current number is the start of a sequence (i.e., num - 1 is not in the set)
For each sequence start, we count the consecutive numbers: 1 is a sequence start and its consecutive numbers are 2, 3, and 4, so the sequence length is $4$
The final output is the maximum sequence length found, which is $4$

Editor

Python 3.13.1

0/0

Run code to see test results.

📘