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05_Consecutive-Array.py
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05_Consecutive-Array.py
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#!/usr/bin/python
# coding=utf-8
'''
__author__ = 'sunp'
__date__ = '2019/1/24'
Given an unsorted array, find the length of the longest sequence of consecutive numbers in the array.
consecutive([4, 2, 1, 6, 5]) = 3, [4, 5, 6]
consecutive([5, 5, 3, 1]) = 1, [1], [3], or [5]
'''
def consecutive1(nums):
# sort and count: O(nlogn) time, O(1) space
if not nums:
return 0
nums.sort()
res, cur = 1, 1
for i in range(1, len(nums)):
if nums[i] - nums[i-1] == 1:
cur += 1
else:
res = max(res, cur)
cur = 1
res = max(res, cur)
return res
def consecutive2(nums):
# hashset: O(n) time, O(n) space
uniques = set(nums)
res = 0
for unique in uniques:
# not the leftmost value in the sequence
if unique - 1 in uniques:
continue
cur = 0
while unique in uniques:
unique, cur = unique + 1, cur + 1
res = max(res, cur)
return res
if __name__ == '__main__':
for consecutive in [consecutive1, consecutive2]:
assert consecutive([]) == 0
assert consecutive([4, 2, 1, 6, 5]) == 3
assert consecutive([5, 5, 3, 1]) == 1