## Longest Consecutive Sequence

### 描述

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.

### 代码

// Longest Consecutive Sequence
// Time Complexity: O(n)，Space Complexity: O(n)
public class Solution {
public int longestConsecutive(int[] nums) {
final HashSet<Integer> mySet = new HashSet<Integer>();
for (int i : nums) mySet.add(i);

int longest = 0;
for (int i : nums) {
int length = 1;
for (int j = i - 1; mySet.contains(j); --j) {
mySet.remove(j);
++length;
}
for (int j = i + 1; mySet.contains(j); ++j) {
mySet.remove(j);
++length;
}
longest = Math.max(longest, length);
}
return longest;
}
}