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57 lines
1.2 KiB
Plaintext
57 lines
1.2 KiB
Plaintext
---
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title: '128. Longest Consecutive Sequence'
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description: Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence
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icon: dot
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topics:
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- { name: "Array", slug: "array" }
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- { name: "Hash Table", slug: "hash-table" }
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- { name: "Union-Find", slug: "union-find" }
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issue: "https://github.com/prdlk/leetcode/issues/34"
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sidebar:
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label: 'Longest Consecutive Sequence'
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badge: 'Medium'
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---
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::::warning
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You must write an algorithm that runs in O(n) time.
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::::
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### Example 1:
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- Input: `nums = [100,4,200,1,3,2]`
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- Output: `4`
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- Explanation: The longest consecutive elements sequence is [1, `2`, `3`, 4]. Therefore its length is `4`.
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### Example 2:
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- Input: `nums = [0,3,7,2,5,8,4,6,0,1]`
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- Output: `9`
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### Example 3:
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- Input: `nums = [1,0,1,2]`
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- Output: `3`
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### Constraints:
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- `0 <= nums.length <= 10^5`
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- `-10^9 <= nums[i] <= 10^9`
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## Solution
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```py
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class Solution:
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def longestConsecutive(self, nums: list[int]) -> int:
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seen = set(nums)
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best = 0
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for n in seen:
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if n - 1 in seen:
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continue
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length = 1
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while length + n in seen:
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length += 1
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best = max(length, best)
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return best
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```
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