![9
Linked list vs. array
• Algorithm to print list values:
ListNode front = ...;
ListNode current = front;
while (current != null) {
System.out.println(current.data);
current = current.next;
}
• Similar to array code:
int[] a = ...;
int i = 0;
while (i < a.length) {
System.out.println(a[i]);
i++;
}](https://image.slidesharecdn.com/10-linked-list-230404091827-5bfb8de9/85/10-linked-list-ppt-9-320.jpg)
10-linked-list.ppt
- 1. CSE 143 Lecture 10 Linked List Basics reading: 16.1 - 16.2 slides created by Marty Stepp http://www.cs.washington.edu/143/
- 2. 2 References vs. objects variable = value; a variable (left side of = ) is an arrow (the base of an arrow) a value (right side of = ) is an object (a box; what an arrow points at) • For the list at right: – a.next = value; means to adjust where points – variable = a.next; means to make variable point at data next 10 a data next 20 1 2 1 2
- 3. 3 Reassigning references • when you say: – a.next = b.next; • you are saying: – "Make the variable a.next refer to the same value as b.next." – Or, "Make a.next point to the same place that b.next points." data next 10 a data next 20 data next 30 b data next 40
- 4. 4 Linked node question • Suppose we have a long chain of list nodes: – We don't know exactly how long the chain is. • How would we print the data values in all the nodes? data next 10 data next 990 list ... data next 20
- 5. 5 Algorithm pseudocode • Start at the front of the list. • While (there are more nodes to print): – Print the current node's data. – Go to the next node. • How do we walk through the nodes of the list? list = list.next; // is this a good idea? data next 10 data next 990 list ... data next 20
- 6. 6 Traversing a list? • One (bad) way to print every value in the list: while (list != null) { System.out.println(list.data); list = list.next; // move to next node } – What's wrong with this approach? • (It loses the linked list as it prints it!) data next 10 data next 990 list ... data next 20
- 7. 7 A current reference • Don't change list. Make another variable, and change that. – A ListNode variable is NOT a ListNode object ListNode current = list; • What happens to the picture above when we write: current = current.next; data next 10 data next 990 list ... data next 20 current
- 8. 8 Traversing a list correctly • The correct way to print every value in the list: ListNode current = list; while (current != null) { System.out.println(current.data); current = current.next; // move to next node } – Changing current does not damage the list. data next 10 data next 990 list ... data next 20
- 9. 9 Linked list vs. array • Algorithm to print list values: ListNode front = ...; ListNode current = front; while (current != null) { System.out.println(current.data); current = current.next; } • Similar to array code: int[] a = ...; int i = 0; while (i < a.length) { System.out.println(a[i]); i++; }
- 10. 10 A LinkedIntList class • Let's write a collection class named LinkedIntList. – Has the same methods as ArrayIntList: •add, add, get, indexOf, remove, size, toString – The list is internally implemented as a chain of linked nodes • The LinkedIntList keeps a reference to its front as a field •null is the end of the list; a null front signifies an empty list front add(value) add(index, value) indexOf(value) remove(index) size() toString() LinkedIntList ListNode ListNode ListNode data next 42 data next -3 data next 17 element 0 element 1 element 2
- 11. 11 LinkedIntList class v1 public class LinkedIntList { private ListNode front; public LinkedIntList() { front = null; } methods go here } front = LinkedIntList
- 12. 12 Implementing add // Adds the given value to the end of the list. public void add(int value) { ... } – How do we add a new node to the end of a list? – Does it matter what the list's contents are before the add? front = data next 42 data next -3 data next 17 element 0 element 1 element 2
- 13. 13 Adding to an empty list • Before adding 20: After: – We must create a new node and attach it to the list. front = front = data next 20 element 0
- 14. 14 The add method, 1st try // Adds the given value to the end of the list. public void add(int value) { if (front == null) { // adding to an empty list front = new ListNode(value); } else { // adding to the end of an existing list ... } }
- 15. 15 Adding to non-empty list • Before adding value 20 to end of list: • After: front = data next 42 data next -3 front = data next 42 data next -3 data next 20 element 0 element 1 element 2 element 0 element 1
- 16. 16 Don't fall off the edge! • To add/remove from a list, you must modify the next reference of the node before the place you want to change. – Where should current be pointing, to add 20 at the end? – What loop test will stop us at this place in the list? front = data next 42 data next -3 element 0 element 1
- 17. 17 The add method // Adds the given value to the end of the list. public void add(int value) { if (front == null) { // adding to an empty list front = new ListNode(value); } else { // adding to the end of an existing list ListNode current = front; while (current.next != null) { current = current.next; } current.next = new ListNode(value); } }
- 18. 18 Implementing get // Returns value in list at given index. public int get(int index) { ... } – Exercise: Implement the get method. front = data next 42 data next -3 data next 17 element 0 element 1 element 2
- 19. 19 The get method // Returns value in list at given index. // Precondition: 0 <= index < size() public int get(int index) { ListNode current = front; for (int i = 0; i < index; i++) { current = current.next; } return current.data; }
- 20. 20 Implementing add (2) // Inserts the given value at the given index. public void add(int index, int value) { ... } – Exercise: Implement the two-parameter add method. front = data next 42 data next -3 data next 17 element 0 element 1 element 2
- 21. 21 The add method (2) // Inserts the given value at the given index. // Precondition: 0 <= index <= size() public void add(int index, int value) { if (index == 0) { // adding to an empty list front = new ListNode(value, front); } else { // inserting into an existing list ListNode current = front; for (int i = 0; i < index - 1; i++) { current = current.next; } current.next = new ListNode(value, current.next); } }