How should I practice Longest Consecutive Sequence?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Amazon phone screen problems in FastPrep.

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FastPrep tags this as a Amazon phone screen coding practice problem when the problem catalog has that company and stage context.

Longest Consecutive Sequence

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Problem statement

Given an unsorted integer array, return the length of its longest sequence of consecutive integer values. Values need not appear consecutively in the input, and duplicate values count once.

The algorithm should run in expected linear time.

Function

longestConsecutive(nums: int[]) → int

Examples

Example 1

nums = [100,4,200,1,3,2]return = 4

The sequence 1,2,3,4 has length four.

Example 2

nums = [0,3,7,2,5,8,4,6,0,1]return = 9

The sequence zero through eight has length nine.

Example 3

nums = []return = 0

Empty input has length zero.

Constraints

0 <= nums.length <= 100000.
Values fit in a signed 32-bit integer.