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0025-reverse-nodes-in-k-group.cpp
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0025-reverse-nodes-in-k-group.cpp
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#include <iostream>
using namespace std;
/**
* 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) {}
};
ListNode* reverseLinkedListTillN(ListNode *head, int n) {
if (head == NULL || head -> next == NULL)
{
return head;
}
ListNode *prev = NULL;
ListNode *elem = head;
ListNode *next = head->next;
int count = 0;
while (next != NULL && count < n)
{
next = elem->next;
elem->next = prev;
prev = elem;
elem = next;
count++;
}
return prev;
}
class Solution
{
public:
ListNode *reverseKGroup(ListNode *head, int k)
{
ListNode *kth_ptr = head->next;
ListNode *zero_ptr = head;
ListNode *zero_prev = nullptr;
int covered = 1;
while (kth_ptr != nullptr)
{
kth_ptr = kth_ptr->next;
covered++;
if (covered == k)
{
ListNode *group_head = reverseLinkedListTillN(zero_ptr, k);
if (zero_prev == nullptr) {
head = group_head;
} else {
zero_prev -> next = group_head;
}
zero_ptr -> next = kth_ptr;
zero_prev = zero_ptr;
zero_ptr = kth_ptr;
covered = 0;
}
}
return head;
}
};
void traverse(ListNode *l)
{
while (l != NULL)
{
cout << l->val;
l = l->next;
}
}
int main()
{
ListNode *a7 = new ListNode(9);
ListNode *a6 = new ListNode(8);
ListNode *a5 = new ListNode(7);
ListNode *a4 = new ListNode(6);
ListNode *a3 = new ListNode(5);
ListNode *a2 = new ListNode(4);
ListNode *a1 = new ListNode(3);
a1->next = a2;
a2->next = a3;
a3->next = a4;
a4->next = a5;
a5->next = a6;
a6->next = a7;
// a7 -> next = a4;
traverse(a1);
cout << endl;
ListNode *ans = (new Solution())->reverseKGroup(a1, 3);
traverse(ans);
cout << endl;
}