# Count pairs in array whose sum is divisible by K

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 .
Note : This question is generalised version of this

Examples:

Input : A = {2, 2, 1, 7, 5, 3}, K = 4 Output : 5 Explaination : There are five pairs possible whose sum is divisible by ‘4’ i.e., (2, 2), (1, 7), (7, 5), (1, 3) and (5, 3) Input : A = {5, 9, 36, 74, 52, 31, 42}, K = 3 Output : 7

i try to write the code but the output is wronge…

``````function pair_sum(arr::Vector{T}, k::Integer) where T<:Integer

sum = 0
for i in length(arr)
for j = 1:length(arr)
merge_both = arr[i] + arr[j]
if mod(merge_both, k) == 0
sum +=1
end
end
end
return sum
end
arr = [5,9,36,74,52,31,42]
println("Total pairs   " , pair_sum(arr, 3))
``````

The for loop in it is not exactly correct. It should be:

``````for i in 1:length(arr)
for j in (i+1):length(arr)
...
end
end
``````

This question might also be better in the Usage (First Steps) rather than Development category.

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