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Review for Exam 1

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Example of the same function written with both forward and reverse accumulation: sumbig.scm (New and improved! With alternate implementations now!)

Example of the speed increase gained by using forward accumulation: speed_test.scm

Example of processing a list of abstract data structures: pizzalist.scm

Example of multiple accumulators: sumlast2.scm

Example of using both forward and reverse accumulation in the same function:

Consider the problem of detecting if a list contains any duplicate elements in a list. In pseudo-code we see:

• Base case: false -- there are no duplicates in an empty list
• Inductive case: Return true if either
  • first is to be found in the rest of the list --> need helper, forward accumulation process
        OR
  • there are duplicates in the rest of the list --> straight recursive call --> reverse accumulation process

   

The key is to write exactly what you think is supposed to be happening: duplicates.scm

 

 

 

©2003 Stephen Wong