Count pairs in array divisible by K
Medium Accuracy: 52.81% Submissions: 2316 Points: 4

Given an array A[] and positive integer K, the task is to count total number of pairs in the array whose sum is divisible by K.

Example 1:

Input :
A[] = {2, 2, 1, 7, 5, 3}, K = 4
Output : 5
Explanation :
There are five pairs possible whose sum
is divisible by '4' i.e., (2, 2),
(1, 7), (7, 5), (1, 3) and (5, 3)

Example 2:

Input :
A[] = {5, 9, 36, 74, 52, 31, 42}, K = 3
Output : 7
Explanation :
There are seven pairs whose sum is divisible by 3,
i.e, (5, 9), (9, 36), (74, 52), (36, 42), (74, 31),
(31, 5) and (5, 52).

You don't have to read input or print anything. Your task is to complete the function countKdivPairs() which takes the array, it's size and an integer K as input and returns the count of pairs whose sum is divisible by K.

Expected Time Complexity : O(n)
Expected Auxiliary Space : O(k)

Constraints :
1 <= N <=10^6
1 <= A[i] <= 10^6
1 <= K <= 100

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