## Assignment 23 — list manipulating functions

### Module aid.py

• Complete the implementation of three functions. Simple tester program abet.py is available to help you test your module `aid` functions.
• None of your functions should get input or print output.
• Examine and think about algorithms for the problems. However, do not write any code before class.

#### Function `rotate( x )`

• Updates list `x` by moving the last element of list `x` (if any) to the beginning of list `x`. This type of list transformation is often called a circular shift.
• In carrying out its action, the function neither returns a new list nor prints anything — it only modify the contents of list `x` in place (e.g., by list-modification methods like `pop()`, `append()`, and `insert()`, or by directly modifying individual elements of list `x`.
• The following code segment from abet.py demonstrates it usage.

x1 = []

x2 = [ 3 ]

x3 = [ 3, 1, 4, 1, 5, 9 ]

x4 = [ 'p', 'e', 'c', 'u', 'l', 'a', 't', 'i', 'o', 'n', 's' ]

aid.rotate( x1 ) ; print( x1 )

aid.rotate( x2 ) ; print( x2 )

aid.rotate( x3 ) ; print( x3 )

aid.rotate( x4 ) ; print( x4 )

• The segment produces as output:

[]



[9, 3, 1, 4, 1, 5]

['s', 'p', 'e', 'c', 'u', 'l', 'a', 't', 'i', 'o', 'n']

#### Function `rotate_k_times( x, k )`

• Updates list `x` by performing `k` circular shifts.
• In carrying out its action, the function neither returns a new list nor prints anything — it only modify the contents of the list `x` in place. The following code segment from abet.py demonstrates it usage.

x1 = []

x2 = [ 3 ]

x3 = [ 3, 1, 4, 1, 5, 9 ]

x4 = [ 'p', 'e', 'c', 'u', 'l', 'a', 't', 'i', 'o', 'n', 's' ]

aid.rotate_k_times( x1, 2 ) ; print( x1 )

aid.rotate_k_times( x2, 3 ) ; print( x2 )

aid.rotate_k_times( x3, 4 ) ; print( x3 )

aid.rotate_k_times( x4 ,5 ) ; print( x4 )

• The segment produces as output:

[]



[4, 1, 5, 9, 3, 1]

['t', 'i', 'o', 'n', 's', 'p', 'e', 'c', 'u', 'l', 'a']

#### Function `common( x, y )`

• Returns a new list whose elements are those elements in `x` that are also in `y`. The ordering of elements in the return list should reflect their ordering in `x`.
• The function does not modify parameters `x` and `y` in any way.
• The following code segment from abet.py demonstrates it usage.

x1 = [] ; y1 = []

x2 = [ 3 ] ; y2 = []

x3 = [ 1 ] ; y3 = [ 3, 1, 4 ]

x4 = [ 2, 7, 1, 8, 2, 8, 1, 8 ] ; y4 = [ 2, 8, 4, 5, 9, ]

z = aid.common( x1, y1 ) ; print( z )

z = aid.common( x2, y2 ) ; print( z )

z = aid.common( x3, y3 ) ; print( z )

z = aid.common( x4, y4 ) ; print( z )

• The segment produces as output:

[]

[]



[2, 8, 2, 8, 8]