概述：
左耳朵耗子专栏《左耳听风》 用户自发每周完成一个ARTS：
1.Algorithm：每周至少做一个 leetcode 的算法题
2.Review：阅读并点评至少一篇英文技术文章
3.Tip：学习至少一个技术技巧
4.Share：分享一篇有观点和思考的技术文章
Algorithm
题目概述：
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：
public class LongestConsecutiveSequence {
public int longestConsecutive(int[] num) {
if (num == null || num.length == 0) {
return 0;
}
if (num.length == 1) {
return 1;
}
HashSet<Integer> hashSet = new HashSet<>();
for (int i : num) {
hashSet.add(i);
}
int maxCount = 1;
for (int n : num) {
if (hashSet.remove(n)) {
int bigVal = n + 1;
int smallVal = n - 1;
int count = 1;
while (hashSet.remove(smallVal)) {
smallVal--;
count++;
}
while (hashSet.remove(bigVal)) {
bigVal++;
count++;
}
maxCount = Math.max(maxCount, count);
}
}
return maxCount;
}
public static void main(String[] args) {
LongestConsecutiveSequence lcs = new LongestConsecutiveSequence();
int result = lcs.longestConsecutive(null);
System.out.println(result);
}
}
