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