Interview Question for Software Engineer at Amazon.com:

Hash table, use all numbers in first list ask keys with a common initial value say 1, then do a individual look-up for each number in the second list, if no such key was found then this number is non-identical, if found key, then increase value to 2, finally, go through all keys in the hash table and check their value, all the keys with value 1 are non-identical, should be a O(n) algorithm