struct ListNode* reverseKGroup(struct ListNode* head, int k) {
struct ListNode *begin;
struct ListNode *tail;
struct ListNode root;
struct ListNode *prev;
int i;
root.next = head;
prev = &root;
while(head){
i = 1;
begin = head;
while(head && i < k){
head = head->next;
i++;
}
if(head == NULL)
goto out;
tail = head->next;
head->next = NULL;
prev->next = reverseNode(begin);
prev = begin;
prev->next = tail;
head = prev->next;
}
out:
return root.next;
}
ListNode* reverseKGroup(ListNode* head, int k) {
if(head == NULL || k<=1) {
return head;
}
ListNode* cur = head, *pre=head, *next;
int m=1;
while(m < k && cur) {
m++;
cur = cur->next;
}
if(cur) {
next = cur->next;
cur->next = NULL;
pre = reverseNode(head);
ListNode *tail = pre;
while(tail->next) {
tail = tail->next;
}
tail->next = reverseKGroup(next, k);
}
return pre;
}
ListNode* reverseKGroup(ListNode* head, int k) {
ListNode* startNode = head, *endNode = head,*pPre = head, *pNext,*result = head;
int IsFirstTime = 1,i;
if(k <= 1 || head == NULL || head->next == NULL)
return head;
//at least has 2 elements
while(startNode!=NULL){
endNode = startNode;
for(i = 1;i<k;i++){
if(endNode->next == NULL)
break;
endNode = endNode->next;
}
//if this is the first time to reverse and there are not enough element in the list
if(i!=k)
break;
pNext = endNode->next;
reverseNode(startNode,endNode);
if(IsFirstTime ==1){
result = endNode;
IsFirstTime =0;
pPre = startNode;
}else{
pPre->next = endNode;
pPre =startNode;
}
startNode->next = pNext;
startNode = pNext;
}
return result;
}
