Longest Consecutive Sequence

Problem

Return the length of the longest run of consecutive integers in the list.

Put all values in a set, then only start counting from a value x when x - 1 is absent; extend upward while consecutive values exist. Every value is visited at most twice, so the algorithm runs in linear time.

Return 0 for an empty list.

Hint

Only begin a run when the previous integer is missing to avoid rescanning runs.

Test cases

case 1

in: [[100,4,200,1,3,2]]

expected: 4

case 2

in: [[]]

expected: 0

case 3

in: [[1,2,0,1]]

expected: 3

case 4

in: [[5]]

expected: 1

case 5

in: [[10,5,12,3,55]]

expected: 1

Starter codePython

def longest_consecutive(nums):
    # Your code here
    pass

5 test cases · run your code against them in the editor