# Longest Consecutive Sequence in Python

PythonServer Side ProgrammingProgramming

Suppose we have an array of integers. We have to find the length of the longest consecutive elements sequence. So if the input is like [100, 4, 250, 1, 3, 2], answer will be 4, as the longest consecutive sequence is [1,2,3,4].

To solve this, we will follow these steps −

• make the array set, longest := 0

• for i in range array −

• if i – 1 is not in a −

• current := i, streak := 0

• while i in a −

• increase i by 1, increase streak by 1

• longest := max of longest and streak

• return longest

## Example

Let us see the following implementation to get a better understanding −

Live Demo

class Solution(object):
def longestConsecutive(self, a):
a = set(a)
longest = 0
for i in a:
if i-1 not in a:
current = i
streak = 0
while i in a:
i+=1
streak+=1
longest = max(longest,streak)
return longest

ob = Solution()
print(ob.longestConsecutive([100,4,250,1,3,2]))

## Input

[100,4,250,1,3,2]

## Output

4