Leetcode-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.

Solution:

public class Solution {
    public int longestConsecutive(int[] num) {

       Set<Integer> set = new HashSet<Integer>();
       for (int i=0;i<num.length;i++) set.add(num[i]);       
       int maxLen = 0;
       int index = 0;
       while (index<num.length){
           if (!set.contains(num[index])){
               index++;
               continue;
           }

           int len =0;
           int val = num[index];
           while (set.contains(val)){
               set.remove(val);
               len++;
               val--;
           }
           val = num[index]+1;
           while (set.contains(val)){
               set.remove(val);
               len++;
               val++;
           }
           if (maxLen<len) maxLen=len;
           index++;
       }
       

       return maxLen;
        
    }

}