pointers and data structures 1 yinzhi cao modified from slides made by prof goce trajcevski
TRANSCRIPT
![Page 1: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/1.jpg)
Pointers and Data Structures
1
Yinzhi Cao
Modified from slides made by Prof Goce Trajcevski
![Page 2: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/2.jpg)
Q & A?
Q: Who am I? A: Yinzhi Cao One of your TAs … I mostly do research in web security. I have a web page ( http://www.cs.northwestern.edu/~yca179 )
Q: Why am I here? A: Prof Henschen is away…
Q: What do we learn today? Linked list. Before that, let me tell you a true story.
2
![Page 3: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/3.jpg)
A true story
When? 2009.
Where? My office.
What happens? My officemate was interviewing Facebook He was asked to program on Facebook wall.
1. Creating a linked list. 2. Deleting a node from a linked list. 3. Deciding whether the linked list contains loop or not?
3
![Page 4: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/4.jpg)
That is what we are going to learn in this class
4
![Page 5: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/5.jpg)
Recall: Array Representation of Sequences
Requires an estimate of the maximum size of the list waste space + always need to track/update “size”
insert and delete: have prohibitive overheads when the sequences are sorted (or, if we insist on inserting at a given location…) e.g. insert at position 0 (making a new element)
requires first pushing the entire array down one spot to make room
e.g. delete at position 0 requires shifting all the elements in the list up one
On average, half of the lists needs to be moved for either operation
5
![Page 6: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/6.jpg)
First, define a Node.
Pointer Implementation (Linked List)
6
a
struct Node {double data; // dataNode*next; // pointer to next
};
“self-referentiality”
![Page 7: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/7.jpg)
Second, linked them together.
7
a b c
Node * A;
(*A).next = B;
Node * B;
(*B).next = C;
Node * C;
(*C).next = NULL;
A->next = B; B->next = C; C->next = NULL;
We want a new symbol
![Page 8: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/8.jpg)
What does the memory look like?
8
a1 a2 a3 a4
a1 800 a2 712 a3 992 a4 0MemoryContent
MemoryAddress 1000 800 712 992
![Page 9: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/9.jpg)
Then we ask:
How to change the list? Inserting a new node. Deleting a node. Finding a node / displaying nodes.
9
![Page 10: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/10.jpg)
Inserting a node
What if I only want to use a pointer that points to A?
10
newNode
a c
bB->next = C;
A->next = B;B->next = p->next;p->next = B;
p
![Page 11: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/11.jpg)
Inserting a node
What if we switch those two operation? No
11
newNode
a c
bB->next = p->next;
p->next = B;
p
![Page 12: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/12.jpg)
However, what if we want to insert in the front?
12
![Page 13: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/13.jpg)
Option One
Deal with it differently.
13
a
Head
b c
![Page 14: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/14.jpg)
Option Two
Add a faked node. It is always there (even for an empty linked list)
14
a
Head
b c
![Page 15: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/15.jpg)
Deleting a Node
15
a b c
A->next = C;
delete B;
![Page 16: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/16.jpg)
Finding a node.
16
a b c
p = p->next;p
d g…
if (p->data == G)…
…
![Page 17: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/17.jpg)
More Practice
How do I delete A?
17
A B C
p->data = p->next->data;
delete B;
D
p
p->next = p->next->next;
B
![Page 18: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/18.jpg)
Comparison with array
18
Compared to the array implementation, the pointer implementation uses only as much space as is needed for the elements currently on the listbut requires extra-space for the pointers in each cell
![Page 19: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/19.jpg)
Backup
19
![Page 20: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/20.jpg)
Pointer Implementation (Linked List)
Ensure that the sequence is stored “on demand” use a linked list a series of “compounds” that are not necessarily adjacent in memory,
borrowed when needed from the Heap…
Each node contains the element and a pointer to a structure containing its successor
the last cell’s next link points to NULL
Compared to the array implementation, the pointer implementation uses only as much space as is needed for the elements currently on the listbut requires extra-space for the pointers in each cell 20
![Page 21: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/21.jpg)
Linked Lists
A linked list is a series of connected nodesEach node contains at least A piece of data (any type) Pointer to the next node in the list
Head: pointer to the first nodeThe last node points to NULL
A
data pointer
node
A
Head
B C
a1 a2 a3 a4
a1 800 a2 712 a3 992 a4 0MemoryContent
MemoryAddress 1000 800 712 992
21
![Page 22: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/22.jpg)
Linked Lists
So, where is the “self-referentiality”
struct Node {double data; // dataNode*next; // pointer to next
};
Now, to have an access to the very first node in the list, we needa variable whose type will exactly be “pointer to a Node”…
Node* headPtr;
22
![Page 23: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/23.jpg)
Printing the elements in a Linked List
void PrintList(Node* ptrToHead) Print the data of all the elements Print the number of the nodes in the list
void DisplayList(Node* ptrToHead){ int num = 0; Node* currNode = ptrToHead; while (currNode != NULL){
cout << currNode->data << endl;currNode = currNode->next;num++;
} cout << "Number of nodes in the list: " << num << endl;}
Accessing a component of a structure, when that structureis assigned to a pointer-variable
23
![Page 24: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/24.jpg)
Typical Algorithms for Lists
Operations of List IsEmpty: determine whether or not the list is empty InsertNode: insert a new node at a particular position FindNode: find a node with a given value DeleteNode: delete a node with a given value DisplayList: print all the nodes in the list
24
![Page 25: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/25.jpg)
Inserting a new node
Node* InsertNode(int index, double x) Insert a node with data equal to x after the index’th elements. (i.e.,
when index = 0, insert the node as the first element; when index = 1, insert the node after the first element, and so on) If the insertion is successful, return the inserted node. Otherwise, return NULL. (If index is < 0 or > length of the list, the insertion will fail.)
Steps1. Locate index’th element2. Allocate memory for the new node3. Point the new node to its successor4. Point the new node’s predecessor to the new node
newNode
index’th element
25
![Page 26: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/26.jpg)
Inserting a new node
Possible cases of InsertNode1. Insert into an empty list
2. Insert in front
3. Insert at back
4. Insert in middle
But, in fact, only need to handle two cases Insert as the first node (Case 1 and Case 2) Insert in the middle or at the end of the list (Case 3 and Case 4)
26
![Page 27: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/27.jpg)
Inserting a new node
Node* InsertNode(int index, double x) {if (index < 0) return NULL;
int currIndex = 1;Node* currNode = head;while (currNode && index > currIndex) {
currNode = currNode->next;currIndex++;
}if (index > 0 && currNode == NULL) return NULL;
Node* newNode = new Node;newNode->data = x;if (index == 0) {
newNode->next = head;head = newNode;
}else {
newNode->next = currNode->next;currNode->next = newNode;
}return newNode;
}
Try to locate index’th node. If it doesn’t exist, return NULL.
27
![Page 28: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/28.jpg)
Inserting a new node
Node* InsertNode(int index, double x) {if (index < 0) return NULL;
int currIndex = 1;Node* currNode = head;while (currNode && index > currIndex) {
currNode = currNode->next;currIndex++;
}if (index > 0 && currNode == NULL) return NULL;
Node* newNode = new Node;newNode->data = x;if (index == 0) {
newNode->next = head;head = newNode;
}else {
newNode->next = currNode->next;currNode->next = newNode;
}return newNode;
}
Create a new node
28
![Page 29: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/29.jpg)
Inserting a new node
Node* InsertNode(int index, double x) {if (index < 0) return NULL;
int currIndex = 1;Node* currNode = head;while (currNode && index > currIndex) {
currNode = currNode->next;currIndex++;
}if (index > 0 && currNode == NULL) return NULL;
Node* newNode = new Node;newNode->data = x;if (index == 0) {
newNode->next = head;head = newNode;
}else {
newNode->next = currNode->next;currNode->next = newNode;
}return newNode;
}
Insert as first elementhead
newNode
29
![Page 30: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/30.jpg)
Inserting a new node
Node* List::InsertNode(int index, double x) {if (index < 0) return NULL;
int currIndex = 1;Node* currNode = head;while (currNode && index > currIndex) {
currNode = currNode->next;currIndex++;
}if (index > 0 && currNode == NULL) return NULL;
Node* newNode = new Node;newNode->data = x;if (index == 0) {
newNode->next = head;head = newNode;
}else {
newNode->next = currNode->next;currNode->next = newNode;
}return newNode;
}
Insert after currNode
newNode
currNode
30
![Page 31: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/31.jpg)
Finding a node
int FindNode(double x) Search for a node with the value equal to x in the list. If such a node is found, return its position. Otherwise, return 0.
int FindNode(double x) {Node* currNode = head;int currIndex = 1;while (currNode && currNode->data != x) {
currNode = currNode->next;currIndex++;
}if (currNode) return currIndex;return 0; // NOTE: Also common to return
// a pointer of a type Node to // the node holding the element}
31
![Page 32: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/32.jpg)
Deleting a node
int DeleteNode(double x) Delete a node with the value equal to x from the list. If such a node is found, return its position. Otherwise, return 0.
Steps Find the desirable node (similar to FindNode) Release the memory occupied by the found node Set the pointer of the predecessor of the found node to the
successor of the found node
Like InsertNode, there are two special cases Delete first node Delete the node in middle or at the end of the list
32
![Page 33: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/33.jpg)
Deleting a node
int DeleteNode(double x) {Node* prevNode = NULL;Node* currNode = head;int currIndex = 1;while (currNode && currNode->data != x) {
prevNode = currNode;currNode = currNode->next;currIndex++;
}if (currNode) {
if (prevNode) {prevNode->next = currNode->next;delete currNode;
}else {
head = currNode->next;delete currNode;
}return currIndex;
}return 0;
}
Try to find the node with its value equal to x
33
![Page 34: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/34.jpg)
Deleting a node
int DeleteNode(double x) {Node* prevNode = NULL;Node* currNode = head;int currIndex = 1;while (currNode && currNode->data != x) {
prevNode = currNode;currNode = currNode->next;currIndex++;
}if (currNode) {
if (prevNode) {prevNode->next = currNode->next;delete currNode;
}else {
head = currNode->next;delete currNode;
}return currIndex;
}return 0;
}
currNodeprevNode
Since the spacefor the nodewas allocatedby “new”
34
![Page 35: Pointers and Data Structures 1 Yinzhi Cao Modified from slides made by Prof Goce Trajcevski](https://reader036.vdocuments.site/reader036/viewer/2022062417/5518d00855034638098b4ff8/html5/thumbnails/35.jpg)
Deleting a node
int DeleteNode(double x) {Node* prevNode = NULL;Node* currNode = head;int currIndex = 1;while (currNode && currNode->data != x) {
prevNode = currNode;currNode = currNode->next;currIndex++;
}if (currNode) {
if (prevNode) {prevNode->next = currNode->next;delete currNode;
}else {
head = currNode->next;delete currNode;
}return currIndex;
}return 0;
}
currNodehead
35