Python code

There is an array numbers made on N integer. Each number has at least two digits and its first and last digits are different

You can select a pair of numbers of the last digit of the first selected number is the same as the first digit of the second selected number Calculate the of ways in such a pair of users can be selectant

White a function

def solution $($numbers$)$

that given an array numbers made of N integers, returns the number of ways to select a pair of numbers as described above

Examples

$1.$ Given numbers $=[30,12,29,91]$ the function should return $3.$ The pairs are $(12,29)(29,91)$ and $(91,12)$

$2.$ Given numbers $=[122,21,21,23]$ the function should return $5.$ The pairs are $(122,23),(21,122)$ occuringg twice $(122\mathrm{.}2521,122)$ securing twice. Please note that the same pair of numbers can appear multiple times if the pairs of the indices are different

Witte an efficient algorithm for the following assumptions

N is an integer within the range $[1..\mathrm{.}100000]$;

each element of array uers is an integer within the range $[10..\mathrm{.}1,000,000,000]$

the first and last digits in each element of array users are afferent

the answer does not exceed $1,000,000,000$