25.txt

Reverse Nodes in K groups 

Given a linked list you need to reverse nodes in k groups if number of nodes is less than k, don't reverse

basic reverse is same
ListNode *curr=head,*prev=NULL,*nxt;
while(curr && curr->next){
  nxt=curr->next;
  curr->next=prev;
  prev=curr;
  curr=nxt;
}
return prev;


Solution

int get_Length(ListNode *head){
    if(!head){
        return 0;
    }
    int len=0;
    while(head){
        len++;
        head=head->next;
    }
    return len;
}
ListNode* reverseKGroup(ListNode* head, int k) {
    ListNode *curr=head,*prev=NULL,*nxt;
    int len=get_Length(head);
    if(len<k || !head){
        return head;
    }
    int n=k;
    while(curr && n--){
        nxt=curr->next;
        curr->next=prev;
        prev=curr;
        curr=nxt;
    }
    if(head){
        head->next=reverseKGroup(nxt,k);
    }
    return prev;
}