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.
这道题其实并没有太多思路，看到好的解法中用了set。判断值是否在set集合中的速度明显要比list快的多, 因为查找set用到了hash，时间在O(1)级别。
class Solution(object):
def longestConsecutive(self, nums):
"""
:type nums: List[int]
:rtype: int
"""
length =
0
nums = set(nums)
for x
in nums:
if x-
1 not in nums:
y = x+
1
while y
in nums:
y = y +
1
length = max(length, y-x)
return length
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