class  {
    public int longestConsecutive(int[] nums) {
        if(nums.length == 0){
            return 0;
        }
        HashSet<Integer> numSet = new HashSet();
        for(int x : nums){
            numSet.add(x);
        }
        int res = 1;
        for(int i = 0; i < nums.length; i++){
            if(!numSet.contains(nums[i])){
                continue;
            }
            numSet.remove(nums[i]);
            int pre = nums[i] - 1;
            int next = nums[i] + 1;
            while(numSet.contains(pre)){
                numSet.remove(pre);
                pre--;
            }
            while(numSet.contains(next)){
                numSet.remove(next);
                next++;
            }
            res = res > next - pre -1 ? res : next - pre -1;
        }
        return res;
    }
}