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.

LongestConsecutive.java

public int longestConsecutive(int[] nums) {
    Map<Integer, Integer> map = new HashMap<>();
    int max = 0;

    for(int i = 0; i < nums.length; i++) {
        if(map.containsKey(nums[i]))
            continue;

        int left = map.getOrDefault(nums[i]-1, 0);
        int right = map.getOrDefault(nums[i]+1, 0);
        int sum = left + right + 1;

        max = Math.max(max, sum);

        map.put(nums[i] - left, sum);
        map.put(nums[i] + right, sum);
        map.put(nums[i], sum);
    }

    return max;
}