1. Hash Tables
   1. Are hash tables just trees?
      1. use hash function to "distribute" the key space
         1. takes some luck to get a good distribution
      2. "hashed key space" may be segmented (essence of a tree structure)
         1. branching factor is proportional to the size of key space
            1. "constant search time" is only achieved when the table size is not much smaller than key space size
         2. most significant "difference" on upper level nodes
         3. examples