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# Longest Consecutive Sequence in Python

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 −

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

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