Design your implementation of the linked list. You can choose to use the singly linked list or the 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 these functions in your linked list class:
get(index): Get the value of theindex-th node in the linked list. If the index is invalid, return-1.addAtHead(val): Add a node of valuevalbefore the first element of the linked list. After the insertion, the new node will be the first node of the linked list.addAtTail(val): Append a node of valuevalto the last element of the linked list.addAtIndex(index, val): Add a node of valuevalbefore theindex-th node in the linked list. Ifindexequals 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.deleteAtIndex(index): Delete theindex-th node in the linked list, if the index is valid.
Example:
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 linkedList = new MyLinkedList(); // Initialize empty LinkedList linkedList.addAtHead(1); linkedList.addAtTail(3); linkedList.addAtIndex(1, 2); // linked list becomes 1->2->3 linkedList.get(1); // returns 2 linkedList.deleteAtIndex(1); // now the linked list is 1->3 linkedList.get(1); // returns 3
Constraints:
0 <= index,val <= 1000- Please do not use the built-in LinkedList library.
- At most
2000calls will be made toget,addAtHead,addAtTail,addAtIndexanddeleteAtIndex.
class ListNode:
def __init__(self, val=0, next=None):
self.val = val
self.next = next
class MyLinkedList:
def __init__(self):
"""
Initialize your data structure here.
"""
self.dummy = ListNode()
self.count = 0
def get(self, index: int) -> int:
"""
Get the value of the index-th node in the linked list. If the index is invalid, return -1.
"""
if index < 0 or index >= self.count:
return -1
cur = self.dummy.next
for _ in range(index):
cur = cur.next
return cur.val
def addAtHead(self, val: int) -> None:
"""
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.
"""
self.addAtIndex(0, val)
def addAtTail(self, val: int) -> None:
"""
Append a node of value val to the last element of the linked list.
"""
self.addAtIndex(self.count, val)
def addAtIndex(self, index: int, val: int) -> None:
"""
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.
"""
if index > self.count:
return
pre = self.dummy
for _ in range(index):
pre = pre.next
pre.next = ListNode(val, pre.next)
self.count += 1
def deleteAtIndex(self, index: int) -> None:
"""
Delete the index-th node in the linked list, if the index is valid.
"""
if index < 0 or index >= self.count:
return
pre = self.dummy
for _ in range(index):
pre = pre.next
t = pre.next
pre.next = t.next
t.next = None
self.count -= 1
# Your MyLinkedList object will be instantiated and called as such:
# obj = MyLinkedList()
# param_1 = obj.get(index)
# obj.addAtHead(val)
# obj.addAtTail(val)
# obj.addAtIndex(index,val)
# obj.deleteAtIndex(index)class MyLinkedList {
private class ListNode {
int val;
ListNode next;
ListNode(int val) {
this(val, null);
}
ListNode(int val, ListNode next) {
this.val = val;
this.next = next;
}
}
private ListNode dummy;
private int count;
/** Initialize your data structure here. */
public MyLinkedList() {
dummy = new ListNode(0);
count = 0;
}
/** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
public int get(int index) {
if (index < 0 || index >= count) {
return -1;
}
ListNode cur = dummy.next;
while (index-- > 0) {
cur = cur.next;
}
return cur.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. */
public void addAtHead(int val) {
addAtIndex(0, val);
}
/** Append a node of value val to the last element of the linked list. */
public void addAtTail(int val) {
addAtIndex(count, val);
}
/** 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. */
public void addAtIndex(int index, int val) {
if (index > count) {
return;
}
ListNode pre = dummy;
while (index-- > 0) {
pre = pre.next;
}
pre.next = new ListNode(val, pre.next);
++count;
}
/** Delete the index-th node in the linked list, if the index is valid. */
public void deleteAtIndex(int index) {
if (index < 0 || index >= count) {
return;
}
ListNode pre = dummy;
while (index-- > 0) {
pre = pre.next;
}
ListNode t = pre.next;
pre.next = t.next;
t.next = null;
--count;
}
}
/**
* 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);
*/