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) {        HashMap<Integer, Integer> hs = new HashMap<Integer, Integer>();        for(int i: num){            hs.put(i, 0);        }        int maxl = 1;        for(int i: num){            if (hs.get(i) == 1) continue;            int tmp = i;            int current_max = 1;            while(hs.containsKey(tmp+1)){                current_max ++;                tmp ++;                hs.put(tmp, 1);            }            tmp = i;            while(hs.containsKey(tmp-1)){                current_max ++;                tmp --;                hs.put(tmp, 1);            }            maxl = Math.max(current_max, maxl);        }        return maxl;    }