Problem Longest Consecutive Sequence

Problem Description:

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

For example,
Given [100, 4, 200, 1, 3, 2],
The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.

Your algorithm should run in O(n) complexity.

 

Solution:

    public int longestConsecutive(int[] num) {
        Set<Integer> set = new HashSet<Integer>();
        
        for (int e : num) {
            set.add(e);
        }
        int max = 1;
        for (int e : num) {
            int left = e -1;
            int right = e + 1;
            int count = 1;

            while (set.contains(left)) {
                count++;
                set.remove(left);
                left--;
            }

            while (set.contains(right)) {
                count++;
                set.remove(right);
                right++;
            }

            max = Math.max(max, count);
        }

        return max;
    }