I want to implement a method that deletes all occurences of a certain value given as argument.
I created 2 temporary elements and referenced them to the head and I will be browsing the list using them. I was able to write a whole code but I’m not getting any result, I don’t know where the problem is, neither I am getting an error.
Any help would be appreciated.
This is the method (my approach):
public void deleteAllOccurrences(int value) {
Element cur = this.head;
Element prev = null;
//deleting head
while(cur != this.rear && cur.data == value) {
cur.next = this.head;
cur = this.head;
}
while(cur != this.rear) {
while(cur != this.rear && cur.data != value) {
prev = cur;
cur = cur.next;
}
if(cur == this.rear)
return;
prev.next = cur.next;
cur = prev.next;
}
}
An this is the whole class maybe you need to check something:
public class CircularLinkedList {
class Element{
int data; // int type used as example
Element next; // reference of the successor
Element(int value) {
this.data = value;
this.next = this;
}
}
private Element head = null;
private Element rear = null;
public CircularLinkedList() {
this.head = this.rear = null;
}
public boolean isEmpty() {
return head == null;
}
public boolean findValue(int value) {
Element cur = this.head;
while(cur != null) {
if (cur.data == value)
return true;
cur = cur.next;
}
return false;
}
public int countValue(int value) {
int c = 0; // counter
Element cur = this.head;
if(cur == null)
return 0;
do {
if(cur.data == value)
c++;
cur = cur.next;
}while (cur != this.head);
return c;
}
@Override
public String toString() {
String str = "";
Element cur = this.head;
if(cur == null)
return "The list is empty";
do {
str += cur.data + " | ";
cur = cur.next;
}while (cur != this.head);
return str;
}
public void insert(int value) {
Element tmp = new Element (value);
//special case: empty list
if(this.head == null) {
this.head = tmp;
}else { // general case
tmp.next = this.head.next;
this.head.next = tmp;
}
}
public void deleteAtHead() {
if(this.head == null) {
return;
}
else {
if(this.head != this.rear) {
this.head = this.head.next;
this.rear.next = this.head;
}
else {
this.head = this.rear = null;
}
}
}
public boolean delete(int value) {
Element cur = this.head;
if(this.head.data == value) { //if the node to be deleted is head node
while(cur.next != this.head) { //iterate till the last node i.e. the node which is pointing to head
cur = cur.next;
}
cur.next = cur.next.next; // update current node pointer to next node of head
this.head = this.head.next; //update head node
return true;
}
else { // if node to be deleted is other than head node
Element prev = cur; // track previous node from current (node)
while(cur.data != value) { // find the node
prev = cur;
cur = cur.next;
}
prev.next = cur.next; //updating next field of previous node to next of current node.current node deleted
return true;
}
}
public void deleteEven() {
// if(this.head == null)
// return;
//
// //case of deleting the head
// if(this.head.data % 2 == 0) {
// this.head.next = this.head;
// this.rear.next = this.head;
// if(this.head == null)
// this.rear = null;
// }
//
// Element cur = this.head;
// Element prev = cur;
// while(cur != this.head) {
// prev = cur;
// cur = cur.next;
// }
// prev.next = cur.next;
if(this.head == null)
return;
Element cur = this.head;
while(cur != this.rear) {
if(cur.data % 2 == 0)
this.delete(cur.data);
cur = cur.next;
}
}
public void deleteLastOccurence(int value) {
Element cur = this.head;
Element prev = null;
Element tmp = null;
if(this.head == null)
return;
if(this.head.data == value) {
this.head = null;
return;
}
while(cur != this.rear) {
if(cur.next != null && cur.next.data == value) {
prev = cur;
tmp = cur.next;
}
cur = cur.next;
}
prev.next = tmp.next;
}
public void deleteAllOccurrences(int value) {
Element cur = this.head;
Element prev = null;
//deleting head
while(cur != this.rear && cur.data == value) {
cur.next = this.head;
cur = this.head;
}
while(cur != this.rear) {
while(cur != this.rear && cur.data != value) {
prev = cur;
cur = cur.next;
}
if(cur == this.rear)
return;
prev.next = cur.next;
cur = prev.next;
}
}
// public CircularLinkedList union(CircularLinkedList a, CircularLinkedList b) {
//
// }
//
//
// public CircularLinkedList inter(CircularLinkedList a, CircularLinkedList b) {
//
// }
public int countOddNbrs() {
if(this.head == null)
return 0;
int c = 0;
Element cur = this.head;
do {
if(cur.data % 2 != 0)
c++;
cur = cur.next;
}while(cur != this.head);
return c;
}
// public int findLastOccurence(int value) {
//
// }
public static void main(String[] args) {
CircularLinkedList list = new CircularLinkedList();
list.insert(8);
list.insert(2);
list.insert(4);
list.insert(3);
list.insert(10);
list.insert(5);
list.insert(-8);
list.insert(4);
System.out.println(list);
// System.out.println(list.findValue(2)); // working
// list.delete(2); // working
// System.out.println(list);
// System.out.println(list.countOddNbrs()); //working
// list.deleteEven(); // not working
// System.out.println(list);
// list.deleteAtHead(); // not working
// System.out.println(list);
// list.deleteLastOccurence(4); //not working
// System.out.println(list);
list.deleteAllOccurrences(4);
System.out.println(list);
}
}
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Answer
your method is running to an infinite loop. Try something like this:
public void deleteAllOccurrences(int value) {
Element cur = this.head;
Element next = null;
if (cur.data == value) {
cur = cur.next;
this.head = cur;
}
do {
next = cur.next;
if (next.data == value) {
cur.next = next.next;
}
cur = next;
} while (cur != this.head);
}
You should handle the corner cases too when the head is the removable element.