Lab 10 Notes

Review: How to Write a Recursive Function

1. Define the function header, including the parameters
2. Define the recursive case
3. Define the base case
4. Put it all together

Implementing a recursive minimum

Let’s develop a recursive implementation for min, named rec_min, that takes as a parameter a non-empty list (i.e., the input has at least one element):

1. Define the function header, including the parameters

   def rec_min(a_list)
   """
   Returns the minimum value in a non-empty list
   """
   
   

2. Define the recursive case

   The minimum value is the lesser of the first element and the recursive minimum of the rest of the list, i.e.

    min_rest = rec_min(a_list[1:])
    if min_rest < a_list[0]:
        return min_rest
    else:
        return a_list[0]
   

3. Define the base case

   The minimum value of a list of length 1 is just the one and only value in the list

4. Put it all together

    def rec_min(a_list):
        if len(a_list) == 1:
            return a_list[0]
        else:
            min_rest = rec_min(a_list[1:])
            if min_rest < a_list[0]:
                return min_rest
            else:
                return a_list[0]