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LESSON 362 OF 671 · HASH TABLE

Longest Consecutive Sequence

Practice O(n)

You get an array nums of integers, in no particular order.

Return the length of the longest run of consecutive values.

Consecutive values go up by 1 each time. For example, 5, 6 and 7 form a run of length 3.

The values of a run can be anywhere in nums. A value that appears more than once counts only once.

Example 1:

Input: nums = [9, 13, 10, 5, 11, 6]
Output: 3
Explanation: 9, 10 and 11 make the longest run.
5 and 6 make a shorter run.
13 stands alone.

Example 2:

Input: nums = [-2, 0, -1, 0, 2, -1]
Output: 3
Explanation: The longest run is -2, -1 and 0.
0 and -1 appear twice, but each counts once.
2 is not in the run, because 1 is missing.

Example 3:

Input: nums = [40, 10, 30, 20]
Output: 1
Explanation: No two values are 1 apart.
So every run has just one value.

Constraints:

  • nums has 1 to 30,000 integers.
  • Each value is from -100 to 100,000,000.

Note:

Your algorithm should run in O(n) time and use O(n) extra space.


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