How to insert an Element in a doubly linked list without repetion? - doubly-linked-list

Question

I am trying to write a code that inserts an Element in a doubly linked list without repetition but it's not working.
Any help would be appreciated.
This is my code:
public void insert(int value) {
Element tmp = new Element(value);
if(this.head == null) {
this.head = this.rear = tmp;
return ;
}
if(this.head.data < value) {
tmp.next = this.head;
this.head.previous = tmp;
tmp.previous = null;
this.head = tmp;
return ;
}
if(this.rear.data > value) {
tmp.previous = this.rear;
this.rear.next = tmp;
this.rear = tmp;
return ;
}
else {
Element cur = this.head;
while(cur.next != null && cur.next.data > value)
cur = cur.next;
tmp.next = cur.next;
tmp.previous = cur;
cur.next.previous = tmp;
cur.next = tmp;
}
return ;
}

Answer 1

You should add a second method:
public boolean isInList(int value) {
Element cur = this.head;
if(this.head == null)
return false;
while(cur != null) {
if(cur.data == value)
return true;
cur = cur.next;
}
return false;
}
And then add it to the insert method:
public void insert(int value) {
Element tmp = new Element(value);
if(this.isInList(value))
return false;
if(this.head == null) {
this.head = this.rear = tmp;
return ;
}
if(this.head.data < value) {
tmp.next = this.head;
this.head.previous = tmp;
tmp.previous = null;
this.head = tmp;
return ;
}
if(this.rear.data > value) {
tmp.previous = this.rear;
this.rear.next = tmp;
this.rear = tmp;
return ;
}
else {
Element cur = this.head;
while(cur.next != null && cur.next.data > value)
cur = cur.next;
tmp.next = cur.next;
tmp.previous = cur;
cur.next.previous = tmp;
cur.next = tmp;
}
return ;
}