203.移除链表元素* 707.设计链表*206.反转链表
203.移除链表元素
题目地址 : leetcode.cn/problems/re…
代码 :
/**
* 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;
ListNode* pre;
ListNode* LinkedList_Return;
p = head ;
LinkedList_Return = nullptr;
pre = p;
while( p != nullptr )
{
if(p->val == val)
{
pre->next = p->next;
pre = pre ;
}
else if(LinkedList_Return == nullptr)
{
LinkedList_Return = p;
pre = p; // 要 区分 情况
}
else // 注意 情况 分类
{
pre = p;
}
p = p->next;
}
return LinkedList_Return ;
}
};
707.设计链表
题目地址 : leetcode.cn/problems/de…
代码 :
class MyLinkedList {
public:
struct LinkedList
{
int val;
LinkedList * next;
};
LinkedList * head = nullptr ;
int length_LinkedList;
MyLinkedList() {
length_LinkedList = 0;
}
int get(int index) {
LinkedList * p ;
p = head ;
int count_Index = 0;
if(index < 0 || index >= length_LinkedList)
{
return -1 ;
}
while( p != nullptr && count_Index < index )
{
p = p->next;
count_Index++;
}
if(count_Index < index )
{
return -1;
}
return p->val ;
}
void addAtHead(int val) {
if(head == nullptr)
{
LinkedList * temp = (LinkedList *) malloc (sizeof (LinkedList));
temp->val = val;
temp->next = nullptr;
head = temp;
}
else
{
LinkedList * p = head;
LinkedList * temp = (LinkedList *) malloc (sizeof (LinkedList));
temp->val = val;
temp->next = head;
head = temp;
}
length_LinkedList++ ;
}
void addAtTail(int val) {
if(head == nullptr)
{
LinkedList * temp = (LinkedList *) malloc (sizeof (LinkedList));
temp->val = val;
temp->next = nullptr;
head = temp;
}
else
{
LinkedList * p = head;
LinkedList * temp = (LinkedList *) malloc (sizeof (LinkedList));
temp->val = val;
temp->next = nullptr;
while(p->next != nullptr )
{
p = p->next ;
}
p->next = temp ;
}
length_LinkedList++ ;
}
void addAtIndex(int index, int val) {
int count_Index;
LinkedList * p = head ;
LinkedList * pre = nullptr ;
count_Index = 0;
//cout << "length_LinkedList : "<<length_LinkedList<<endl;
if(index < 0 || index > length_LinkedList)
{
return ;
}
if( index == 0 )
{
addAtHead(val);
return ;
}
else if( (index ) == length_LinkedList)
{
addAtTail(val);
return ;
}
while( p != nullptr && count_Index < index )
{
pre = p;
p = p->next ;
count_Index++;
}
if(count_Index < index )
{
cout<<" 输入 的 index 超出 了 链表 长度 " << endl ; // 在 其它 函数 部分 正常 工作 时
}
LinkedList * temp = (LinkedList *) malloc (sizeof (LinkedList));
temp->val = val;
temp->next = p ;
pre->next = temp;
length_LinkedList++ ;
}
void deleteAtIndex(int index) {
int count_Index;
LinkedList * p = head ;
LinkedList * pre = nullptr ;
count_Index = 0;
if(index < 0 || index >= length_LinkedList)
{
return ;
}
if( index == 0 )
{
head = p->next ;
length_LinkedList-- ;
return ;
}
else if( (index + 1 ) == length_LinkedList )
{
while(p->next != nullptr )
{
pre = p;
p = p->next;
}
pre->next = nullptr;
length_LinkedList-- ;
return ;
}
//cout<< "p->val : " << p->val << endl;
while( p != nullptr && count_Index < index )
{
pre = p ;
//cout<< "p->val : " << p->val << endl;
p = p->next ;
count_Index++;
//cout<<"line"<<endl;
}
//cout<< "p->val : " << p->val << endl;
//if(pre == nullptr)
//{
// cout<< 1 << endl;
//}
//if(p == nullptr)
//{
// cout<< 2 << endl;
//}
pre->next = p->next ;
length_LinkedList-- ;
}
};
/**
* 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
题目地址 : leetcode.cn/problems/re…
代码 : (”头插法“)
/**
* 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* p1;
ListNode* p2 = nullptr;
ListNode* ptr_NewLinkedListHead = nullptr;
ListNode* next = nullptr;
ListNode* Node_Temp = nullptr;
p1 = head;
while( p1 != nullptr )
{
next = p1 -> next ;
if(p2 == nullptr )
{
Node_Temp = p1;
// 末尾 指针 的 清理
Node_Temp -> next = nullptr ;
p2 = Node_Temp ;
ptr_NewLinkedListHead = p2;
}
else
{
Node_Temp = p1;
Node_Temp -> next = ptr_NewLinkedListHead;
ptr_NewLinkedListHead = Node_Temp;
}
p1 = next;
}
return ptr_NewLinkedListHead ;
}
};
代码 : （“使用 Stack 的 支持” ）
/**
* 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) {
// 使用 栈 的 support ?
ListNode* p1 = head;
ListNode* p2 = nullptr ;
ListNode* ptr_NewLinkedListHead = nullptr;
stack<int> stack_Temp;
while(p1 != nullptr )
{
stack_Temp.push(p1->val);
//cout<< 1 << endl;
//cout<< stack_Temp.top() << endl;
p1 = p1->next ;
}
//while( stack_Temp.size() != 0)
while( stack_Temp.empty() == 0)
{
//cout<< stack_Temp.top() << endl;
int num_Temp = stack_Temp.top();
stack_Temp.pop();
//ListNode* Node_Temp = (ListNode*)malloc(sizeof(ListNode));
ListNode* Node_Temp = new ListNode(num_Temp);
Node_Temp->val = num_Temp ;
Node_Temp->next = nullptr ;
// 分 情况
if(p2 == nullptr)
{
p2 = Node_Temp;
ptr_NewLinkedListHead = p2 ;
}
else
{
p2->next = Node_Temp;
p2 = p2->next ;
}
}
//cout<< 1111 << endl;
//ListNode* p3 = ptr_NewLinkedListHead;
//while(p3 != nullptr )
//{
//cout<<p3->val<<endl;
//p3 = p3->next;
//}
return ptr_NewLinkedListHead ;
}
};
