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Program to find a sublist where first and last values are same in Python

Suppose we have a list of numbers called nums, we have to find the number of sublists where the first element and the last element are same.

So, if the input is like nums = [10, 15, 13, 10], then the output will be 5, as the sublists with same first and last element are: [10], [15], [13], [10], [10, 15, 13, 10].

To solve this, we will follow these steps −

  • num_sublists := size of nums

  • d := an empty map

  • for each n in nums, do

    • d[n] := d[n] + 1

  • for each number k and corresponding frequency v of elements in d, do

    • if v is not same as 1, then

      • num_sublists := num_sublists +(quotient of (v-1) *(v) /2)

  • return num_sublists

Let us see the following implementation to get better understanding −

Example

from collections import defaultdict
class Solution:
   def solve(self, nums):
      num_sublists = len(nums)

      d = defaultdict(int)
      for n in nums:
         d[n] += 1
   
      for k,v in d.items():
         if v != 1:
            num_sublists += (v-1)*(v)//2
      return num_sublists
ob = Solution()
nums = [10, 15, 13, 10]
print(ob.solve(nums))

Input

[10, 15, 13, 10]

Output

5