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.

Solution:

public class Solution {
  public int longestConsecutive(int[] nums) {
    int max = 0;
    Set<Integer> set = new HashSet<Integer>();
    for (int i = 0; i < nums.length; i++) {
      set.add(nums[i]);   
    }
    for (int i = 0; i < nums.length; i++) {
      int count = 1;
      // look left
      int num = nums[i];
      while (set.contains(--num)) {
        count++;
        set.remove(num);
      }
      // look right
      num = nums[i];
      while (set.contains(++num)) {
        count++;
        set.remove(num);
      }
      max = Math.max(max, count);
    }
    return max;
  }
}