Find Longest Consecutive Sequence in an Unsorted?

Short answer: Array int LongestConsecutive(int[] nums)

Example code

{
HashSet<int> set = new HashSet<int>(nums);
int longest = 0;
foreach (int num in set)
{
if (!set.Contains(num - 1)) Follow on: {
int currentNum = num;
int length = 1; while (set.Contains(currentNum + 1)) { currentNum++; length++; }
longest = Math.Max(longest, length);
}
}
return longest;
} Explanation: Check only starts of sequences, count consecutive numbers using HashSet for O(n).

Real-world example (ShopNest)

In coding rounds, state complexity aloud, write a clear ShopNest-flavored example (orders, carts), then handle edge cases (empty list, null, overflow).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.