LeetCode 128 - Longest Consecutive Sequence

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.

public int longestConsecutive(int[] num) {
    if(num==null || num.length<1) return 0;
    HashSet<Integer> set = new HashSet<Integer>(num.length);
    for(int e:num) {
        set.add(e);
    }
    int result = 1;
    for(int e:num) {
        int count = 1;
        int left = e-1;
        int right = e+1;
        while(set.contains(left)) {
            count++;
            set.remove(left--);
        }
        while(set.contains(right)) {
            count++;
            set.remove(right++);
        }
        result = Math.max(result, count);
    }
    return result;
}