Longest Consecutive Sequence
Part of Practice: Beyond the Basics
Given an unsorted array of integers, find the length of the longest run of consecutive values — numbers that follow each other like 1, 2, 3, 4 — that can be formed from the array's elements. The elements do not need to be adjacent in the array, and duplicates do not extend a run.
The required time bound is O(n), which rules out sorting first. The array can be empty and can hold up to 100,000 values.
Examples
- Input:
- nums = [100, 4, 200, 1, 3, 2]
- Output:
- 4
The longest consecutive run is 1, 2, 3, 4 — length 4.
- Input:
- nums = [0, 3, 7, 2, 5, 8, 4, 6, 0, 1]
- Output:
- 9
The values 0 through 8 are all present (the duplicate 0 adds nothing), giving a run of length 9.
- Input:
- nums = []
- Output:
- 0
Hints
One at a time — struggle first, peek second.
Your thinking space — verify on LeetCode, then mark it.