# Share my C++ solutions

• Solution 1.

``````class Solution {
public:
ListNode* reverseKGroup(ListNode* head, int k) {
ListNode* pre = new ListNode(0);
ListNode* res = pre;
while(fast){
int i = k - 1;
while(fast && i--) fast = fast->next;
if(fast){
next = fast->next;
reverse(pre, slow, fast, next);
pre = slow;
slow = next;
fast = next;
}
}
return res->next;
}

void reverse(ListNode* left, ListNode* start, ListNode* end, ListNode* right){
ListNode* pre(left), *cur(start), *next;
ListNode* tmp = start;
while(cur != right){
next = cur->next;
cur->next = pre;
pre = cur;
cur = next;
}
left->next = pre;
tmp->next = right;
}
};
``````

Solution 2.

``````class Solution {
public:
ListNode* reverseKGroup(ListNode* head, int k) {
ListNode dummy(0);
ListNode* pre = &dummy, *cur(head), *next, *tmp, *p, *ppre, *ccur;
while(cur){
p = cur;
for(int i = 1; i < k && p; i++) p = p->next;
if(!p) break;
ppre = pre;
ccur = cur;
pre = p->next;
tmp = p->next;
while(cur != tmp){
next = cur->next;
cur->next = pre;
pre = cur;
cur = next;
}
ppre->next = pre;
pre = ccur;
}
return dummy.next;
}
};
``````

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