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 class LongestConsecutiveSequence {
    public int longestConsecutive(int[] nums) {
        int res = 0;
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
       
        for(int n : nums) {
            if(!map.containsKey(n)) {
                int left = (map.containsKey(n - 1)) ? map.get(n - 1) : 0;
                int right = (map.containsKey(n + 1)) ? map.get(n + 1) : 0;
                int sum = left + right + 1;
                res = Math.max(res, sum);
                map.put(n, sum);
map.put(n - left, sum);
                map.put(n + right, sum);
            } else {
                continue;
            }
        }
        return res;
    }
}