h2. 4sum

bq. Given A, an array of integers, find out if there are any four numbers such that their sum equals zero (you can use the same number more than once). For example given A = [2, 3, 1, 0, -4, -1] a solution is 3 + 1 + 0 - 4 = 0 or 0 + 0 + 0 + 0 = 0.

bq. Given A, an array of integers, find out if there are any four numbers such that their sum equals zero. For example given A = [2, 3, 1, 0, -4, -1] a solution is 3 + 1 + 0 - 4 = 0 or 0 + 0 + 0 + 0 = 0 (you can use the same number more than once).

The naive algorithm tries all the possible combinations of four numbers. This solution takes $O(N^4^)$ time.