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25.cpp
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90 lines (77 loc) · 1.77 KB
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/**
* 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* oh=nullptr;
ListNode* ot=nullptr;
ListNode* th=nullptr;
ListNode* tt=nullptr;
void addfirst(ListNode* node)
{
if(th==NULL)
{
th=node;
tt=node;
}
else
{
node->next=th;
th=node;
}
}
int length(ListNode* head)
{
int l=0;
ListNode* temp=head;
while(temp!=NULL)
{
l++;
temp=temp->next;
}
return l;
}
ListNode* reverseKGroup(ListNode* head, int k) {
if(head==NULL || head->next==NULL || k==0 || k==1 ) return head;
int len=length(head);
if(len<k) return head;
ListNode* curr=head;
while(curr!=NULL)
{
int tk=k;
while(tk-->0)
{
ListNode* fwd=curr->next;
curr->next=NULL;
addfirst(curr);
curr=fwd;
}
len-=k;
if(ot==nullptr)
{
oh=th;
ot=tt;
}
else
{
ot->next=th;
ot=tt;
}
tt=nullptr;
th=nullptr;
if(len<k)
{
ot->next=curr;
curr=nullptr;
}
}
return oh;
}
};