CODE 5: 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.

 

My code:

	public int longestConsecutive(int[] num) {
		// Start typing your Java solution below
		// DO NOT write main() function
		if (null == num || num.length < 0) {
			return 0;
		}
		Map<Integer, Integer> results = new HashMap<Integer, Integer>();
		Set<Integer> used = new HashSet<Integer>();
		int max = 0;
		for (int i = 0; i < num.length; i++) {
			if (used.contains(num[i])) {
				continue;
			} else {
				used.add(num[i]);
			}

			int left = num[i], right = num[i];

			if (results.containsKey(left - 1)
					&& results.get(left - 1) <= left - 1) {
				left = results.get(left - 1);
			}

			if (results.containsKey(right + 1)
					&& results.get(right + 1) >= right + 1) {
				right = results.get(right + 1);
			}
			results.put(left, right);
			results.put(right, left);

			max = max > (right - left + 1) ? max : (right - left + 1);
		}
		return max;
	}