Suppose you are given an integer c and an array, A, indexed from 1 to n, of n
integers in the range from 1 to 5n (possibly with duplicates). Describe an efficient
algorithm for determining if there are two integers, A[i] and A[j], in A that sum
to c, that is, such that c = A[i] + A[j], for 1 ≤ i < j ≤ n. What is the running
time of your algorithm?