Reverse linkedlist in k groups

#1

Can you explain how to do this;
we will reverse k elements in the linkedlist
then ask recursion to the rest
can reverse k element after recursive call or before recursive call or can we do both ways?

#2

questions–>


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* reverseKGroup(ListNode* head, int k) {
        if(head==NULL or head->next==NULL){
            return head;
        }
        ListNode* p=NULL;
        ListNode* n=NULL;
            ListNode* c=head;
        int count=0;
        
        while(c!=NULL and count<k){
            n=c->next;
            c->next=p;
            p=c;
            c=n;
            count++;
            
        }
        
         head->next=reverseKGroup(n,k);
        
        return p;
    }
};

my code is not working when the elements left are less than k ,then according to leetcode we should not reverse them;

#3

okay i got it

/**
 * 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* reverseKGroup(ListNode* head, int k) {
        if(head==NULL or head->next==NULL){
            return head;
        }
        ListNode* p=NULL;
        ListNode* n=NULL;
            ListNode* c=head;
        int count=0;
        ListNode* temp=head;
        while(temp!=NULL){
            count++;
            temp=temp->next;
        }
        if(count<k){
            return head;
        }
        count=0;
        while(c!=NULL and count<k){
            n=c->next;
            c->next=p;
            p=c;
            c=n;
            count++;
            
        }
        
         head->next=reverseKGroup(n,k);
        
        return p;
    }
};

but can explain first doubt?

#4

Hello @sheikhhaji18 you have doubt in reversing linked list in the groups of k?
if you have doubt in that only:


if you have any doubt still you can ask here:
Happy Learning!!

#5

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