Here when I talk about hash table, I mean it is simply an array and it has nothing to do with STL hash map. For example, there is an array, int a[] = {3, 5,6, 7, 11}. The key for hash table could be the elements of array a. What if there is negative item in the array, for example, int a[] = {3, -1, 5, 7, -6}? How'd I build a hash table based on this array? Thanks.