public class Solution {
    public int longestConsecutive(int[] num) {
        if(num==null||num.length==0)
        {
            return 0;
        }
        int result=1;
        HashSet<Integer> set=new HashSet<Integer>();
        Map<Integer,Integer>map=new HashMap<Integer,Integer>();
        for(int element:num)
        {
            set.add(element);
        }
        for(int element:num)
        {
            if(map.containsKey(element))
            {
                continue;
            }
            int end=element;
            for(end=element+1;set.contains(end)&&!map.containsKey(end);end++);
            int len=end-element;
            if(map.containsKey(end))
            {
                len+=map.get(end);
            }
            result=Math.max(len,result);
            for(int i=element;i<end;i++,len--)
            {
                map.put(i,len);
            }
        }
        return result;
    }
}