Lecture 20 — Exercises

Solutions to the problems below must be sent to Submitty for automatic scoring. A separate file must submitted for each problem. Solutions must be submitted by 4 pm on Tuesday, November 15.

For both of these exercises download the file lec20_ex.zip from the course Piazza Resource page. It includes a data file and lec20_ex_start.py. You start from the latter for both exercises. You will notice that the main code in this file requests the name of a data file from the user, opens and reads the file to form a list of values, and then in a loop requests several different values to search for, outputting the result of the function call for each.

1. Write a Python function called linear_search that is given two arguments: a value x and a list L. The function must return the list index of the first location of x in L. If x is not in L the function must return -1. You may use any Python list functions you wish.
2. What if the list is already sorted? Write a modifed version of linear_search that returns the index of the first instance of

x or the index where x should be inserted if it is not in L For example, in the list

L = [ 1.3, 7.9, 11.2, 15.3, 18.5, 18.9, 19.7 ]

the call

linear_search(11.9, L)

should return 3, while the call

linear_search( 20.5, L)

should return 7. You must not use binary search (even though that would be faster — this is an exercise) and you must use either a for or a while loop.