Program to find length of longest consecutive sequence in Python

Suppose we have an unsorted array of numbers, we have to find the length of the longest sequence of consecutive elements.

So, if the input is like nums = [70, 7, 50, 4, 6, 5], then the output will be 4, as the longest sequence of consecutive elements is [4, 5, 6, 7]. so we return its length: 4.

To solve this, we will follow these steps −

• nums := all unique elements of nums

• max_cnt := 0

• for each num in nums, do

  • if num - 1 not in nums, then

    • cnt := 0

    • while num is present in nums, do

      • num := num + 1

      • cnt := cnt + 1

    • max_cnt := maximum of max_cnt and cnt

• return max_cnt

Let us see the following implementation to get better understanding −

Example

 Live Demo

class Solution:
   def solve(self, nums):
      nums = set(nums)
      max_cnt = 0
      for num in nums:
         if num - 1 not in nums:
            cnt = 0
            while num in nums:
               num += 1
               cnt += 1
            max_cnt = max(max_cnt, cnt)
      return max_cnt
ob = Solution()
nums = [70, 7, 50, 4, 6, 5]
print(ob.solve(nums))

Input

[70, 7, 50, 4, 6, 5]

Output

4