Design Linked List
Design your implementation of the linked list. You can choose to use a singly or doubly linked list.
A node in a singly linked list should have two attributes: val
and next
. val
is the value of the current node, and next
is a pointer/reference to the next node.
If you want to use the doubly linked list, you will need one more attribute prev
to indicate the previous node in the linked list. Assume all nodes in the linked list are 0-indexed.
Implement the MyLinkedList
class:
MyLinkedList()
Initializes theMyLinkedList
object.int get(int index)
Get the value of theindexth
node in the linked list. If the index is invalid, return-1
.void addAtHead(int val)
Add a node of valueval
before the first element of the linked list. After the insertion, the new node will be the first node of the linked list.void addAtTail(int val)
Append a node of valueval
as the last element of the linked list.void addAtIndex(int index, int val)
Add a node of valueval
before theindexth
node in the linked list. Ifindex
equals the length of the linked list, the node will be appended to the end of the linked list. Ifindex
is greater than the length, the node will not be inserted.void deleteAtIndex(int index)
Delete theindexth
node in the linked list, if the index is valid.
Example 1:
Input
["MyLinkedList", "addAtHead", "addAtTail", "addAtIndex", "get", "deleteAtIndex", "get"]
[[], [1], [3], [1, 2], [1], [1], [1]]
Output
[null, null, null, null, 2, null, 3]
Explanation
MyLinkedList myLinkedList = new MyLinkedList();
myLinkedList.addAtHead(1);
myLinkedList.addAtTail(3);
myLinkedList.addAtIndex(1, 2); // linked list becomes 1->2->3
myLinkedList.get(1); // return 2
myLinkedList.deleteAtIndex(1); // now the linked list is 1->3
myLinkedList.get(1); // return 3
Constraints:
0 <= index, val <= 1000
Please do not use the built-in LinkedList library.
At most
2000
calls will be made toget
,addAtHead
,addAtTail
,addAtIndex
anddeleteAtIndex
.
Solutions
🧠 Cpp
struct Node
{
Node(int v) : val(v){}
int val;
Node *next = nullptr;
};
class MyLinkedList
{
Node *head = nullptr,
*tail = nullptr;
size_t size = 0;
public:
/** Initialize your data structure here. */
MyLinkedList() = default;
/** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
int get(int index)
{
if(!size || index > size-1)
return -1;
Node *asked_node = head;
//node at index
for(; index != 0; --index)
asked_node = asked_node->next;
return asked_node->val;
}
/** Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list. */
void addAtHead(int val)
{
Node *new_node = new Node(val);
//init
if(!head)
head = tail = new_node;
else
{
new_node->next = head;
head = new_node;
}
size++;
}
/** Append a node of value val to the last element of the linked list. */
void addAtTail(int val)
{
Node *new_node = new Node(val);
//init
if(!head)
head = tail = new_node;
else
{
tail->next = new_node;
tail = new_node;
}
size++;
}
/** Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted. */
void addAtIndex(int index, int val)
{
//index should exist
// or index == size, it`s push_back
if(index > size)
return;
if(index == 0)
addAtHead(val);
else if(index == size)
addAtTail(val);
else
{
Node *new_node = new Node(val),
//one node before insertion position
*prev_node = head;
for(; index != 1; --index)
prev_node = prev_node->next;
new_node->next = prev_node->next;
prev_node->next = new_node;
size++;
}
}
/** Delete the index-th node in the linked list, if the index is valid. */
void deleteAtIndex(int index)
{
//index should exist
if(index > size-1)
return;
if(index == 0)
{
//delete head
Node *head_next = head->next;
if(head == tail)
tail = nullptr;
delete head;
head = head_next;
}
else if(index == size-1)
{
//delete tail
Node *prev_node = head;
//get node before index
for(; index != 1; --index)
prev_node = prev_node->next;
prev_node->next = nullptr;
delete tail;
tail = prev_node;
}
else
{
//delete node in the middle
Node *prev_node = head;
//get node before index
for(; index != 1; --index)
prev_node = prev_node->next;
Node *to_delete = prev_node->next;
prev_node->next = to_delete->next;
delete to_delete;
}
size--;
}
};
/**
* Your MyLinkedList object will be instantiated and called as such:
* MyLinkedList* obj = new MyLinkedList();
* int param_1 = obj->get(index);
* obj->addAtHead(val);
* obj->addAtTail(val);
* obj->addAtIndex(index,val);
* obj->deleteAtIndex(index);
*/
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