leetcode笔记—翻转链表

1、翻转链表

void reverseNodes(ListNode *start, ListNode *end) {   //翻转链表
ListNode *second = start -> next;
ListNode *first = start;
ListNode *temp;

while(second != end) {
temp = second -> next;
second -> next = first;
first = second;
second = temp;
}

second -> next = first;

}     //翻转后start指向最后一个节点

ListNode* revertList(ListNode* head){ //翻转链表
if(head == NULL){
return NULL;
}

ListNode* p = head->next;
head->next = NULL;

while(p != NULL){
ListNode* tmp = p;
p = p->next;
tmp->next = head;
head = tmp;
}
return head;
}

2、链表相邻的k个节点翻转

void reverseNodes(ListNode *start, ListNode *end) {
ListNode *second = start -> next;
ListNode *first = start;
ListNode *temp;

while(second != end) {
temp = second -> next;
second -> next = first;
first = second;
second = temp;
}

second -> next = first;
}

ListNode *reverseKGroup(ListNode *head, int k) {
ListNode *tempHead = head, *tempEnd = head;
ListNode *result = head;
ListNode *preEnd = head;
ListNode *temp = NULL;
bool flag = true;
int count = 1;

if(!head) {
return NULL;
}

while(tempEnd -> next) {
tempEnd = tempEnd -> next;
count++;

if(count == k) {
temp = tempEnd -> next;
if(flag) {
flag = false;
result = tempEnd;
reverseNodes(tempHead, tempEnd);
tempHead -> next = temp;
count = 1;
}  //翻转第一个k个节点；
else {
preEnd -> next = tempEnd;
preEnd = tempHead;
reverseNodes(tempHead, tempEnd);
tempHead -> next = temp;
count = 1;
}//翻转后面的节点

if(temp) {
tempHead = temp;
tempEnd = temp;
}
else {
tempHead -> next = NULL;
return result;
}
}
}
return result;
}
};

//以上程序是有问题的，不知道哪里错了，下面是个accepted

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* reverseKGroup(ListNode* head, int k) {
ListNode** re=&head;
ListNode* pre=head;
ListNode* q=NULL;
whi
4000
le(true)
{
int i=k;
ListNode* temp=pre;
while(temp!=NULL&&--i>0)
{
temp=temp->next;
}     //取到K个节点的尾
if(temp==NULL) return head;//如果没有K长度，返回
i=k;
while(i--)
{    //翻转
ListNode *p_next=pre->next;
pre->next=q;
q=pre;
pre=p_next;
}
(*re)->next=pre;
ListNode *t=*re;
*re=q;
re=&(t->next);
q=NULL;

}
return head;
}
};