$(1)$ Codewriting

You are given an array of integers and an integer $k.$ Your task is to calculate the number of ways to pick two different indices $a[i]+a[j]ka=[1,2,3,4,5]k=3i,$ such that $a[i]+a[j]is$ divisible $byk.$

Example

For $a=[1,2,3,4,5]$ and $k=3,$ the output should $be$