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:

 1 public class Solution {
 2     public int longestConsecutive(int[] num) {
 3 
 4        Set<Integer> set = new HashSet<Integer>();
 5        for (int i=0;i<num.length;i++) set.add(num[i]);       
 6        int maxLen = 0;
 7        int index = 0;
 8        while (index<num.length){
 9            if (!set.contains(num[index])){
10                index++;
11                continue;
12            }
13 
14            int len =0;
15            int val = num[index];
16            while (set.contains(val)){
17                set.remove(val);
18                len++;
19                val--;
20            }
21            val = num[index]+1;
22            while (set.contains(val)){
23                set.remove(val);
24                len++;
25                val++;
26            }
27            if (maxLen<len) maxLen=len;
28            index++;
29        }
30        
31 
32        return maxLen;
33         
34     }
35 
36 }