CSE1301 Computer Programming: Lecture 30 Linked Lists Part 2

1
CSE1301 Computer Programming Lecture 30Linked
Lists (Part 2)
2
Topics

• Sorted linked list
• The free list
• Adding to a linked list
• Deleting from a linked list

3
Recall Linked List

• struct ListElementRec
• int item
• int next
• typedef struct ListElementRec ListElement
• ListElement listmaxListLength
• int first

5
3
4
0
2
END
4
Delete an Item Typical Case
Example Delete item 8
first
1
0
1
2
3
5
4
4
8
2
9
5
3
5
3
4
0
2
END
5
Delete an Item Typical Case (cont)
Example Delete item 8
first
1
0
1
2
3
5
4
4
8
2
9
5
3
5
3
4
0
2
END
6
Delete an Item Typical Case (cont)
Example Delete item 8
first
1
0
1
2
3
5
4
4
8
2
9
5
3
2
5
3
4
2
END
7
Delete an Item Typical Case (cont)
Example Delete item 8
first
1
0
1
2
3
5
4
4
2
9
5
3
5
3
4
2
END
8
Delete the Last Item
Example Delete item 9
first
1
0
1
2
3
5
4
4
2
9
5
3
5
3
4
2
END
9
Delete the Last Item (cont)
Delete last item Delete item 9
Example Delete item 9
first
1
0
1
2
3
5
4
4
2
5
3
9
5
3
4
END
END
10
Delete the Last Item (cont)
Example Delete item 9
first
1
0
1
2
3
5
4
4
2
5
3
5
3
4
END
11
Delete the First Item
Example Delete item 2
first
1
0
1
2
3
5
4
4
2
5
3
5
3
4
END
12
Delete the First Item (cont)
Example Delete item 2
first
5
0
1
2
3
5
4
4
2
5
3
5
3
4
END
13
Delete the First Item (cont)
Example Delete item 2
first
5
0
1
2
3
5
4
4
5
3
3
4
END
14
Filling In the Gaps

• Problem How do we find a free slot if we want
  to insert a new item into the list?

15
Filling In the Gaps Solution 1

• Mark free slots with special value, and perform
  linear search

const int END -1 const int FREE -2
first
1
5
4
0
1
2
3
4
2
3
5
3
END
FREE
FREE
FREE
16
Filling In the Gaps Solution 1 (cont)

• Mark free slots with special value, and perform
  linear search

Example Insert 5 into the linked list
first
1
0
1
2
3
5
4
4
2
3
5
3
END
FREE
FREE
FREE
17
Filling In the Gaps Solution 1 (cont)

• Mark free slots with special value, and perform
  linear search

Example Insert 5 into the linked list
first
1
0
1
2
3
5
4
4
5
2
3
5
3
END
FREE
FREE
FREE
18
Filling In the Gaps Solution 1 (cont)

• Mark free slots with special value, and perform
  linear search

Example Insert 5 into the linked list
first
1
5
4
0
1
2
3
4
5
2
3
0
5
3
FREE
FREE
FREE
19
Filling In the Gaps Solution 1 (cont)

• Mark free slots with special value, and perform
  linear search

Example Insert 5 into the linked list
first
1
0
1
2
3
5
4
4
5
2
3
5
3
0
END
FREE
FREE
20
Filling In the Gaps Solution 1 (cont)

• Mark free slots with special value, and perform
  linear search

Example Insert 5 into the linked list
Problem Linear search for free slots
first
1
0
1
2
3
5
4
4
5
2
3
5
3
0
END
FREE
FREE
21
Filling In the Gaps Solution 2

• Close the gaps after a deletion, and always
  append at the end

Example Delete 4 from the linked list
4
3
5
0
1
2
4
2
9
5
3
4
2
3
1
END
22
Filling In the Gaps Solution 2 (cont)

• Close the gaps after a deletion, and always
  append at the end

Example Delete 4 from the linked list
first
0
5
0
1
2
4
3
4
2
9
5
3
4
2
3
1
END
23
Filling In the Gaps Solution 2 (cont)

• Close the gaps after a deletion, and always
  append at the end

Example Delete 4 from the linked list
first
0
5
0
1
2
4
3
4
2
9
5
3
3
4
3
1
END
24
Filling In the Gaps Solution 2 (cont)

• Close the gaps after a deletion, and always
  append at the end

Example Delete 4 from the linked list
first
0
5
0
1
2
4
3
2
9
5
3
4
3
1
END
25
Filling In the Gaps Solution 2 (cont)

• Close the gaps after a deletion, and always
  append at the end

Example Delete 4 from the linked list
count
first
5
0
4
3
5
0
1
2
2
9
3
2
4
END
26
Filling In the Gaps Solution 2 (cont)

• Close the gaps after a deletion, and always
  append at the end

Example Delete 4 from the linked list
count
first
5
0
4
3
5
0
1
2
2
9
3
4
2
END
27
Filling In the Gaps Solution 2 (cont)

• Close the gaps after a deletion, and always
  append at the end

Example Delete 4 from the linked list
first
0
4
3
5
0
1
2
2
9
3
END
28
Filling In the Gaps Solution 2 (cont)

• Close the gaps after a deletion, and always
  append at the end

Example Delete 4 from the linked list
Problem Moving items and adjusting links
count
first
4
0
4
3
5
0
1
2
3
2
9
3
2
END
29
Filling In the Gaps Solution 3

• Link the free slots together to form a free
  linked list

free
2
first
1
0
1
2
3
4
5
4
2
3
5
3
END
END
0
4
30
Filling In the Gaps Solution 3

• Link the free slots together to form a free
  linked list

To linked list of items
free
2
first
1
5
4
0
1
2
3
4
2
3
5
3
END
END
0
4
31
Filling In the Gaps Solution 3 (cont)

• Link the free slots together to form a free
  linked list

free
To linked list of free elements
2
first
1
5
0
1
2
3
4
4
2
3
5
3
END
END
0
4
32
Initialization

• Begin with empty item list and a full free list

free
0
first
END
5
4
0
1
2
3
2
5
4
END
3
1
33
Adding an Item -- Example 1

• Add item with value 5 (first item)
• Step 1 Ensure free ! END

free
0
first
END
5
4
0
1
2
3
2
5
4
END
3
1
34
Adding an Item -- Example 1 (cont)

• Step 2 Put value 5 in the first free slot
• listfree.item value

free
0
first
END
5
4
0
1
2
3
5
2
5
4
END
3
1
35
Adding an Item -- Example 1 (cont)

• Step 3 Remember position of new item
• firstfree

free
0
first
0
5
4
0
1
2
3
5
2
5
4
END
3
1
36
Adding an Item -- Example 1 (cont)

• Step 4 Update the free linked list to next free
  slot
• free listfree.next

first
0
5
4
0
1
2
3
5
2
5
4
END
3
1
37
Adding an Item -- Example 1 (cont)

• Step 5 Put END marker in new element
• listfirst.next END

first
0
5
4
0
1
2
3
5
2
5
4
END
3
END
38
Adding an Item -- Example 2
Add item with value 9 Step 1 Ensure free !
END
first
0
5
4
0
1
2
3
5
2
5
4
END
3
END
39
Adding an Item -- Example 2 (cont)
Step 2 Put value 9 in the first free slot
listfree.item value
first
0
5
4
0
1
2
3
5
9
2
5
4
END
3
END
40
Adding an Item -- Example 2 (cont)
Step 3 Remember the position of the new item
curr free
first
0
5
4
0
1
2
3
5
9
2
5
4
END
3
END
1
curr
41
Adding an Item -- Example 2 (cont)
Step 4 Update the free linked list to next free
slot free listfree.next
first
0
5
4
0
1
2
3
5
9
2
5
4
END
3
END
1
curr
42
Adding an Item -- Example 2 (cont)
Step 5 Find the position of the preceding
item prev findPrevious(first,value,list)
first
0
5
4
0
1
2
3
5
9
2
5
4
END
3
END
prev
1
0
curr
43
Adding an Item -- Example 2 (cont)
Step 6 Link current item to the next item in the
list listcurr.next listprev.next
first
0
5
4
0
1
2
3
5
9
5
4
END
3
END
prev
1
0
curr
44
Adding an Item -- Example 2 (cont)
Step 7 Insert current item after the previous
item listprev.next curr
first
0
5
4
0
1
2
3
5
9
END
5
4
END
3
1
prev
1
0
curr
45
Adding an Item -- Code
const int END -1 int addItem (int first, int
free, int value, ListElement
list) int curr, prev if (free ! END)
listfree.item value curr free free
listfree.next prev findPrevious(first,
value, list) / assumption the list is never
empty / listcurr.next listprev.next
listprev.next curr return free else
printf(Not enough space\n) exit(1)
46
Exercise 1

• Given the list below, follow the algorithm for
  adding the following items in order
• Add 6 In the middle of list
• Add 3 Becomes new first item in list
• Add an item to an empty list

free
2
first
0
5
4
0
1
2
3
5
9
5
4
END
3
1
END
47
Deleting an Item -- Example

• Delete item with value 3

free
2
first
1
5
4
0
1
2
3
4
2
3
5
3
END
END
0
4
48
Deleting an Item -- Example (cont)

• Step 1 Find position of the item to be deleted
• curr findIndex(first,value,list)

free
2
first
1
5
4
0
1
2
3
4
2
3
5
3
END
END
0
4
curr
5
49
Deleting an Item -- Example (cont)

• Step 2 Ensure the item is in the list
• curr ! END

free
2
first
1
5
4
0
1
2
3
4
2
3
5
3
END
END
0
4
curr
5
50
Deleting an Item -- Example (cont)

• Step 3 Find the position of the previous item
• prev findPrevious(first,value,list)

free
2
first
1
5
4
0
1
2
3
4
2
3
5
3
END
END
0
4
curr
prev
1
5
51
Deleting an Item -- Example (cont)

• Step 4 Bypass the current item in the list
• listprev.next listcurr.next

free
2
first
1
5
4
0
1
2
3
4
2
3
3
3
END
END
0
4
curr
prev
1
5
52
Deleting an Item -- Example (cont)

• Step 5 Link current position to first free slot
• listcurr.next free

free
2
first
1
5
4
0
1
2
3
4
2
3
2
3
END
END
0
4
curr
prev
1
5
53
Deleting an Item -- Example (cont)

• Step 6 Make current position the first free slot
• free curr

first
1
5
4
0
1
2
3
4
2
3
2
3
END
END
0
4
curr
prev
1
5
54
Deleting an Item -- Code
const int END -1 int deleteItem (int first,
int free, int value, ListElement
list) int curr, prev curr findIndex(first,
value, list) / assumption the list is never
empty / if (curr END) printf("d is
NOT in the list\n", value) return free
prev findPrevious(first, value, list) /
assumption the last item is never deleted /
listprev.next listcurr.next
listcurr.next free free curr return
free
55
Exercise 2

• Consider the following cases when deleting
• the first item in the linked list
• the last item in the linked list
• an item that is not in the linked list
• Modify the deleteItem function to allow
• for the deletion of the first item
• for the list to become empty
• Write the algorithm and the C code for
• findIndex() finding the index of the item with a
  given value
• findPrev() finding the index of the item
  previous to a given value

56
Main points

• Linked list
• has an item list and a free list
• makes it easier to add and delete elements
• searching for an element is slow (linear)

57
Reading

• Knuth, Fundamental Algorithms, Section 2.2.3
• pages 251-258 (1st edition)
• pages 254-261 (3rd edition)
• Horowitz and Sahni, Fundamentals of Data
  Structures, Chapter 4, pages 106-112