1. Which approach efficiently finds the longest consecutive elements sequence in an unsorted array of integers?
Difficulty: MediumType: MCQTopic: Longest Consecutive Sequence
Using a hash set you can check for each number whether it is a sequence start (num‐1 absent) then count forwards. This yields O(n) average time. Sorting would take O(n log n).
Example code
Set<Integer> s = new HashSet<>(Arrays.asList(nums)); int longest=0; for(int n:nums){ if(!s.contains(n-1)){ int cur=n; while(s.contains(cur)) cur++; longest = Math.max(longest, cur-n); } }