第二章 链表part01
203.移除链表元素
题目链接： leetcode.cn/problems/re…
Code :
/**
* 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) {
ListNode* p = head;
ListNode* pre;
ListNode* NewHead;
while(p != nullptr && p->val == val)
{
p = p->next;
}
NewHead = p;
pre = p;
while(p != nullptr)
{
//内循环
if(p->val == val)
{
pre->next = p->next;
}
else
{
pre = p;
}
p = p->next;
}
return NewHead;
}
};
707. 设计链表
题目链接： leetcode.cn/problems/de…
Code
class MyLinkedList {
public:
struct node
{
int val;
node * next;
};
// 带头 结点
node * head ;
MyLinkedList() {
head = new node() ;
head->val = 0;
head->next = NULL;
}
int get(int index) {
int i = 0;
//cout<<"------------get--------------------"<<endl;
int step = index + 1;
int count = 0;
node * p;
p = head->next;
//cout<<"index : "<<index<<endl;
//cout<<"step : "<<step<<endl;
//cout<<"head->val : "<<head->val<<endl;
if(step > head->val)
{
return -1;
}
if(step == 1)
{
return p->val;
}
count++;
for( ; i < (step - 1) ; i++ )
{
if(p == NULL)
{
break;
}
p = p->next;
count++;
}
//cout<<"------count : "<<count<<endl;
if(count < (step))
{
return -1;
}else
if(count == step)
{
return p->val;
}
else
{
cout<<"step 溢出"<<endl;
return -1;
}
//cout<<"-----------------------------------"<<endl;
}
void addAtHead(int val) {
node * temp = new node() ;
temp->val = val ;
temp->next = head->next;
head->next = temp;
head->val ++ ;
}
void addAtTail(int val) {
node * p = head->next ;
node * temp = new node();
temp->val = val;
temp->next = NULL;
if(p==NULL)
{
head->next = temp;
head->val++;
}
else
{
while(p->next!=NULL)
{
p = p->next;
}
p->next = temp;
head->val++;
}
}
void addAtIndex(int index, int val) {
int i = 0;
int MoveStep = index + 1;
int count = 0;
node * pre;
node * p = head->next;
count++;
if(index > head->val)
{
return ;
}else
if(index == head->val)
{
addAtTail(val);
}else
if(index == 0)
{
addAtHead(val);
}else
{
for( ; i < MoveStep - 1 ; i++ )
{
if(p == NULL)
{
break;
}
pre = p;
p = p->next;
count++;
}
//cout<<"***********MoveStep - 1 : "<<MoveStep - 1<<endl;
//cout<<"***********count : "<<count<<endl;
//cout<<"***********p->val : "<<p->val<<endl;
//cout<<"***********pre->val : "<<pre->val<<endl;
if(count < (MoveStep))
{
return ;
}else
if(count == MoveStep)
{
node * temp = new node();
temp->val = val;
temp->next = p;
pre->next = temp;
head->val++;
}
else
{
cout<<"step 溢出"<<endl;
}
}
}
void deleteAtIndex(int index) {
node * p = head->next;
node * pre ;
int step = index + 1;
int i = 0;
if(step > head->val )
{
return ;
}
if(index == 0)
{
head->next = head->next->next ;
head->val--;
}
else
{
for( ;i< (step-1) ; i++)
{
pre = p;
p = p->next;
}
pre->next = p->next;
head->val--;
}
}
};
/**
* 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
题目链接： leetcode.cn/problems/re…
Code
/**
* 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) {
// 假设 为 有头 结点
if(head == NULL)
{
return NULL;
}else
if(head->next == NULL)
{
return head; // 一个 有效 结点 时 调 了 之后 前后 一样 (有效 荷载 区)
}else // xx 内容 的 积累
{
// “头插法”
ListNode * p = head;
ListNode * pre = p ;
ListNode * spear ;
p = p->next;
pre->next = NULL;
while(p != NULL)
{
// 内部 操作 ———— 链表 处理
spear = p->next;
p->next = pre;
pre = p;
p = spear;
}
head = pre ;
return head ;
}
}
};
