3.
Stack and Queue Programming
.
Write a method
compressDuplicates
that accepts a stack of integers
as a parameter and that replaces each sequence of duplicates with a pair of values: a count of the number of
duplicates, followed by the actual duplicated number.
For example, suppose a variable called
s
stores the
following sequence of values (duplicates underlined):
bottom [2, 2, 2, 2, 2
, -5, -5
, 3, 3, 3, 3
, 4, 4
, 1, 0, 17, 17
] top
and we make the call of
compressDuplicates(s);
, after the call
s
should store the following values:
bottom [5, 2, 2, -5, 4, 3, 2, 4, 1, 1, 1, 0, 2, 17] top
This new stack indicates that the original had 5 occurrences of 2 at the bottom of the stack followed by 2
occurrences of -5 followed by 4 occurrences of 3, and so on.
This process works best when there are many
duplicates in a row.
For example, if the stack instead had stored:
bottom [10, 20, 10, 20, 20
, 10] top
Then the resulting stack after the call ends up being longer than the original:
bottom [1, 10, 1, 20, 1, 10, 2, 20, 1, 10] top
If the stack is empty, your method should not change it.
You may use one queue as auxiliary storage to
solve this problem.
You may not use any other auxiliary data structures to solve this problem, although you
can have as many simple variables as you like.
You may not use recursion to solve this problem.
For full
credit your code must run in O(
n
) time where
n
is the number of elements of the original stack.
Use the
Queue
interface and
Stack
/
LinkedList
classes discussed in lecture.
You have access to the following two methods and may call them as needed to help you solve the problem: