class Solution {
    public int longestConsecutive(int[] nums) {
       if (nums.length == 0) return 0;
       HashSet<Integer> hs = new HashSet<>();
       for(int num:nums) hs.add(num);
       int longest =1;
       for(int num: nums ){
           //check if the num is the start of a sequence by checking if left exists
           if(!hs.contains(num-1)){ // start of a sequence
                int count =1;
                while(hs.contains(num + 1)){ // check if hs contains next no.
                    num++;
                    count++;
                }
                longest = Math.max(longest, count);
                
           }
           if(longest > nums.length/2) break;

       }
       return longest;
    }
}