Three solutions I gave. 1. Sort the array in O(nlogn). Min and Max as two indices. Count=0 Loop if A[Min]+A[Max]N Decrement (Max) else Increment(Count) End 2. Using extra space and count sort if the minima and maxima of array sets are in a given range. Max absolute negative number subtracted to keep numbers in positive number space. Loop if Memory[N- A[i]- Min] Increment(Count) End 3. Create a Hashset/Hashtable. Look for N-A[i] and increment count if found. Loop if Get(N- A[i]) Increment (Count) else Push(A[i]) End

the complexity of ur solution is not so good you can do better

couldn't you just look through the array and check the sum of each combination and then check against a hashtable?! I don't understand why you have to do all the sorting stuff!