Short Problem Definition:
You are given an array of n integers and a positive integer, k. Find and print the number of (i,j) pairs where i < j and ai + aj is evenly divisible by k.
Link
Complexity:
time complexity is O(N^2)
space complexity is O(1)
Execution:
Brute force search.
Solution:
n,k = raw_input().strip().split(' ')
n,k = [int(n),int(k)]
a = map(int,raw_input().strip().split(' '))
count=0
for i in xrange(len(a)):
for j in xrange(i+1,len(a)):
if (a[i]+a[j]) % k == 0:
count+=1
print count