day03 - 链表part01
203. 移除链表元素
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
ListNode* removeElements(ListNode* head, int val) {
/*
while(head != NULL && head->val == val){
ListNode* tmp = head;
head = head->next;
delete tmp;
}
ListNode* new_head = head;
while(head != NULL){
if(head->next != nullptr && head->next->val == val){
ListNode* tmp = head->next;
head->next = head->next->next;
delete tmp;
}else{
head = head->next;
}
}
return new_head;
*/
//虚拟头结点
ListNode* tmp_head = new ListNode(0);
tmp_head->next = head;
ListNode* cur = tmp_head;
while(cur != NULL){
if(cur->next != nullptr && cur->next->val == val){
ListNode* tmp = cur->next;
cur->next = cur->next->next;
delete tmp;
}else{
cur = cur->next;
}
}
head = tmp_head->next;
delete tmp_head;
return head;
}
};
707. 设计链表
class MyLinkedList {
public:
struct my_list{
int val;
my_list* next;
my_list(int val):val(val),next(nullptr){}
};
MyLinkedList() {
dummy_list = new my_list(0);
_size = 0;
}
void log(){
return;
my_list* tmp = dummy_list;
while(tmp != nullptr){
cout << tmp->val << "," ;
tmp = tmp->next;
}
cout << endl;
}
int get(int index) {
//log();
if(_size == 0 || index < 0 || index >= _size)
return -1;
my_list* tmp = dummy_list->next;
while(index --)
tmp = tmp->next;
return tmp->val;
}
void addAtHead(int val) {
my_list* tmp = new my_list(val);
tmp->next = dummy_list->next;
dummy_list->next = tmp;
_size++;
log();
}
void addAtTail(int val) {
my_list* tmp = dummy_list;
while(tmp->next != NULL)
tmp = tmp->next;
my_list* tmp2 = new my_list(val);
tmp->next = tmp2;
_size++;
log();
}
void addAtIndex(int index, int val) {
//cout << "size:" << _size << endl;
if(index > _size)
return;
my_list* tmp = dummy_list;
while(--index >= 0)
tmp = tmp->next;
//cout << "index:" << index << endl;
my_list* tmp2 = new my_list(val);
if(tmp->next != NULL)
tmp2->next = tmp->next;
tmp->next = tmp2;
_size++;
log();
}
void deleteAtIndex(int index) {
if(index >= _size)
return;
my_list* tmp = dummy_list;
while(--index >= 0)
tmp = tmp->next;
if(index < _size - 1){
my_list* tmp2 = tmp->next;
tmp->next = tmp->next->next;
delete tmp2;
}else{
tmp->next = tmp->next->next;
}
_size--;
log();
}
private:
my_list* dummy_list;
int _size;
};
/*
class MyLinkedList {
public:
// 定义链表节点结构体
struct LinkedNode {
int val;
LinkedNode* next;
LinkedNode(int val):val(val), next(nullptr){}
};
// 初始化链表
MyLinkedList() {
_dummyHead = new LinkedNode(0); // 这里定义的头结点 是一个虚拟头结点，而不是真正的链表头结点
_size = 0;
}
// 获取到第index个节点数值，如果index是非法数值直接返回-1， 注意index是从0开始的，第0个节点就是头结点
int get(int index) {
if (index > (_size - 1) || index < 0) {
return -1;
}
LinkedNode* cur = _dummyHead->next;
while(index--){ // 如果--index 就会陷入死循环
cur = cur->next;
}
return cur->val;
}
// 在链表最前面插入一个节点，插入完成后，新插入的节点为链表的新的头结点
void addAtHead(int val) {
LinkedNode* newNode = new LinkedNode(val);
newNode->next = _dummyHead->next;
_dummyHead->next = newNode;
_size++;
}
// 在链表最后面添加一个节点
void addAtTail(int val) {
LinkedNode* newNode = new LinkedNode(val);
LinkedNode* cur = _dummyHead;
while(cur->next != nullptr){
cur = cur->next;
}
cur->next = newNode;
_size++;
}
// 在第index个节点之前插入一个新节点，例如index为0，那么新插入的节点为链表的新头节点。
// 如果index 等于链表的长度，则说明是新插入的节点为链表的尾结点
// 如果index大于链表的长度，则返回空
// 如果index小于0，则在头部插入节点
void addAtIndex(int index, int val) {
if(index > _size) return;
if(index < 0) index = 0;
LinkedNode* newNode = new LinkedNode(val);
LinkedNode* cur = _dummyHead;
while(index--) {
cur = cur->next;
}
newNode->next = cur->next;
cur->next = newNode;
_size++;
}
// 删除第index个节点，如果index 大于等于链表的长度，直接return，注意index是从0开始的
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;
//delete命令指示释放了tmp指针原本所指的那部分内存，
//被delete后的指针tmp的值（地址）并非就是NULL，而是随机值。也就是被delete后，
//如果不再加上一句tmp=nullptr,tmp会成为乱指的野指针
//如果之后的程序不小心使用了tmp，会指向难以预想的内存空间
tmp=nullptr;
_size--;
}
// 打印链表
void printLinkedList() {
LinkedNode* cur = _dummyHead;
while (cur->next != nullptr) {
cout << cur->next->val << " ";
cur = cur->next;
}
cout << endl;
}
private:
int _size;
LinkedNode* _dummyHead;
};
*/
/**
* 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);
*/
206. 反转链表
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
ListNode* reverseList(ListNode* head) {
ListNode* tmp;
ListNode* pre = NULL;
ListNode* cur = head;
while(cur){
tmp = cur->next;
cur->next = pre;
pre = cur;
cur = tmp;
}
return pre;
}
};