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# Program to count elements whose next element also in the array in Python

Suppose we have a list of numbers say nums, we have to find the number of elements x in the array, such that x + 1 also exists in the array.

So, if the input is like nums = [4, 2, 3, 3, 7, 9], then the output will be 3, because 2+1 = 3 is present, 3+1 = 4 is present and another 3 is present so total 3.

To solve this, we will follow these steps −

answer := 0

c := a list containing frequencies of each elements present in nums

dlist := a list from list of all keys of c

for each i in dlist, do

if c[i + 1] > 0, then

answer := answer + c[i]

return answer

## Example

Let us see the following implementation to get better understanding

from collections import Counter def solve(nums): answer = 0 c = Counter(nums) dlist = list(c.keys()) for i in dlist: if c[i + 1] > 0: answer += c[i] return answer nums = [4, 2, 3, 3, 7, 9] print(solve(nums))

## Input

[4, 2, 3, 3, 7, 9]

## Output

3

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