day15【LeetCode力扣】707.设计链表
day15【LeetCode力扣】707.设计链表
1.题目描述
你可以选择使用单链表或者双链表，设计并实现自己的链表。
单链表中的节点应该具备两个属性：val 和 next 。val 是当前节点的值，next 是指向下一个节点的指针/引用。
如果是双向链表，则还需要属性 prev 以指示链表中的上一个节点。假设链表中的所有节点下标从 0 开始。
实现 MyLinkedList 类：
MyLinkedList()初始化MyLinkedList对象。int get(int index)获取链表中下标为index的节点的值。如果下标无效，则返回-1。void addAtHead(int val)将一个值为val的节点插入到链表中第一个元素之前。在插入完成后，新节点会成为链表的第一个节点。void addAtTail(int val)将一个值为val的节点追加到链表中作为链表的最后一个元素。void addAtIndex(int index, int val)将一个值为val的节点插入到链表中下标为index的节点之前。如果index等于链表的长度，那么该节点会被追加到链表的末尾。如果index比长度更大，该节点将 不会插入 到链表中。void deleteAtIndex(int index)如果下标有效，则删除链表中下标为index的节点。
示例：
输入
["MyLinkedList", "addAtHead", "addAtTail", "addAtIndex", "get", "deleteAtIndex", "get"]
[[], [1], [3], [1, 2], [1], [1], [1]]
输出
[null, null, null, null, 2, null, 3]
2.题解
2.1单链表法
c++版本
class MyLinkedList {
public:
struct LinkedList{
int val;
LinkedList* next;
LinkedList(int val):val(val),next(nullptr){}
};
MyLinkedList() {
_dummynode=new LinkedList(0);
_size=0;
}
int get(int index) {
if(index>_size-1||index<0)
return -1;
LinkedList* cur=_dummynode->next;
while(index--){
cur=cur->next;
}
return cur->val;
}
void addAtHead(int val) {
LinkedList *newnode = new LinkedList(val);
newnode->next=_dummynode->next;
_dummynode->next=newnode;
_size++;
}
void addAtTail(int val) {
LinkedList* newnode=new LinkedList(val);
LinkedList* cur=_dummynode;
while(cur->next!=nullptr){
cur=cur->next;
}
cur->next=newnode;
_size++;
}
void addAtIndex(int index, int val) {
if(index>_size)
return;
if(index<0)
index=0;
LinkedList *newnode=new LinkedList(val);
LinkedList* cur=_dummynode;
while(index--){
cur=cur->next;
}
newnode->next=cur->next;
cur->next=newnode;
_size++;
}
void deleteAtIndex(int index) {
if(index>=_size||index<0)
return;
LinkedList* cur=_dummynode;
while(index--){
cur=cur->next;
}
LinkedList* tmp=cur->next;
cur->next=cur->next->next;
delete tmp;
tmp=nullptr;
_size--;
}
void printLinkedList(){
LinkedList* cur=_dummynode;
while(cur->next!=nullptr){
cout<<cur->next->val<<" ";
cur=cur->next;
}
cout<<endl;
}
private:
int _size;
LinkedList *_dummynode;
};
python版本
class ListNode:
def __init__(self,val=0,next=None):
self.val=val
self.next=next
class MyLinkedList:
def __init__(self):
self.dummy_head=ListNode()
self.size=0
def get(self, index: int) -> int:
if index<0 or index>=self.size:
return -1
cur = self.dummy_head.next
for i in range(index):
cur=cur.next
return cur.val
def addAtHead(self, val: int) -> None:
newcode=ListNode(val,self.dummy_head.next)
self.dummy_head.next=newcode
self.size+=1
def addAtTail(self, val: int) -> None:
newcode=ListNode(val)
cur=self.dummy_head
while cur.next:
cur=cur.next
cur.next=newcode
self.size+=1
def addAtIndex(self, index: int, val: int) -> None:
if index<0 or index>self.size:
return
cur=self.dummy_head
for i in range(index):
cur=cur.next
cur.next=ListNode(val,cur.next)
self.size+=1
def deleteAtIndex(self, index: int) -> None:
if index>=self.size or index<0:
return
cur = self.dummy_head
for i in range(index):
cur=cur.next
cur.next=cur.next.next
self.size-=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)
大家仔细分析下代码，很容易就理解了，不过需要多练习，需要自己手动写出来，加油⛽️
2.2双链表法
python
class ListNode:
def __init__(self,val=0,prev=None,next=None):
self.val=val
self.prev=prev
self.next=next
class MyLinkedList:
def __init__(self):
self.head=None
self.tail=None
self.size=0
def get(self, index: int) -> int:
if index<0 or index>=self.size:
return -1
if index<self.size//2:
current=self.head
for i in range(index):
current=current.next
else:
current=self.tail
for i in range(self.size- index-1):
current=current.prev
return current.val
def addAtHead(self, val: int) -> None:
new_node=ListNode(val,None,self.head)
if self.head:
self.head.prev=new_node
else:
self.tail=new_node
self.head=new_node
self.size+=1
def addAtTail(self, val: int) -> None:
new_node=ListNode(val,self.tail,None)
if self.tail:
self.tail.next=new_node
else:
self.head=new_node
self.tail=new_node
self.size+=1
def addAtIndex(self, index: int, val: int) -> None:
if index < 0 or index > self.size:
return
if index == 0:
self.addAtHead(val)
elif index == self.size:
self.addAtTail(val)
else:
if index < self.size // 2:
current = self.head
for i in range(index - 1):
current = current.next
else:
current = self.tail
for i in range(self.size - index):
current = current.prev
new_node = ListNode(val,current,current.next)
current.next.prev = new_node
current.next = new_node
self.size += 1
def deleteAtIndex(self, index: int) -> None:
if index<0 or index>=self.size:
return
if index==0:
self.head=self.head.next
if self.head:
self.head.prev=None
else:
self.tail=None
elif index==self.size-1:
self.tail=self.tail.prev
if self.tail:
self.tail.next=None
else:
self.head=None
else:
if index<self.size//2:
current=self.head
for i in range(index):
current=current.next
else:
current=self.tail
for i in range(self.size-index-1):
current=current.prev
current.prev.next=current.next
current.next.prev=current.prev
self.size-=1