203.移除链表元素
class Solution {
public:
ListNode* removeElements(ListNode* head, int val) {
ListNode *dummyHead = new ListNode(0);
dummyHead->next = head;
ListNode *cur = dummyHead;
while (cur->next != nullptr) {
if (cur->next->val == val) {
ListNode *tmp = cur->next;
cur->next = cur->next->next;
delete tmp;
}else {
cur = cur->next;
}
}
return dummyHead->next;
}
};
707.设计链表
class MyLinkedList {
public:
struct LinkedNode {
int val;
LinkedNode* next;
LinkedNode(int val) : val(val), next(nullptr){}
};
MyLinkedList() {
_dummyHead = new LinkedNode(0);
_size = 0;
}
int get(int index) {
if ((_size - 1) < index || index < 0) return -1; //先排除下标无效情况
LinkedNode *cur = _dummyHead->next;
while (index--) {
cur = cur->next;
}
return cur->val;
}
void addAtHead(int val) {
LinkedNode *newNode = new LinkedNode(val);
newNode->next = _dummyHead->next;
_dummyHead->next = newNode;
++_size;
} // 这里不要忘记size++
void addAtTail(int val) {
LinkedNode *cur = _dummyHead;
while (cur->next != nullptr) {
cur = cur->next;
}
LinkedNode *newNode = new LinkedNode(val);
cur->next = newNode;
++_size;
}
void addAtIndex(int index, int val) {
if (index > _size) return;
if(index < 0) index = 0;
LinkedNode *cur = _dummyHead;
while (index--) {
cur = cur->next;
}
LinkedNode *newNode = new LinkedNode(val);
newNode->next = cur->next;
cur->next = newNode;
_size++;
}
void deleteAtIndex(int index) {
if (index >= _size || index < 0) {
return;
}
LinkedNode *cur = _dummyHead;
while (index--) {
cur = cur->next;
}
LinkedNode* tmp = cur->next;
cur->next = cur->next->next;
delete tmp;
tmp=nullptr;
_size--;
}
void printLinkedList() {
LinkedNode *cur = _dummyHead;
while (cur->next != nullptr) {
cout << cur->next->val << " ";
cur = cur->next;
}
cout << endl;
}
private:
int _size;
LinkedNode *_dummyHead;
};
206.反转链表
class Solution {
public:
ListNode* reverse(ListNode* pre, ListNode* cur) {
if (cur == nullptr) return pre;
ListNode* tmp = cur->next;
cur->next = pre;
return reverse(cur, tmp);
}
ListNode* reverseList(ListNode* head) {
return reverse(nullptr, head);
}
};