... ARITHMETIC Dictionaries help speed algorithms e.g put all substrings into set, looking for duplicates - Θ(n2 ) operations Lecture Hashing I: Chaining, Hash Functions 6.006 Spring 2008 How we solve the ... would need to be stored in an array, indexed by key φ key item key item key item Figure 1: Direct-access table Problems: keys must be nonnegative integers (or using two arrays, integers) large ... dictionary • hash function h: U → φ, 1, , m − T φ k1 U k k k kk k3 h(k 1) = k2 m-1 Figure 2: Mapping keys to a table • two keys ki , kj � K collide if h(ki ) = h(kj ) How we deal...