0025-reverse-nodes-in-k-group.cs

/**
 * Definition for singly-linked list.
 * public class ListNode {
 * public int val;
 * public ListNode next;
 * public ListNode(int val=0, ListNode next=null) {
 * this.val = val;
 * this.next = next;
 * }
 * }
 */
publicclassSolution
{
publicListNodeReverseKGroup(ListNodehead,intk)
{
vardummy=newListNode(0,head);
vargroupPrev=dummy;
vargroupNext=dummy;

while(true)
{
varkth=getKth(groupPrev,k);
if(kth==null)
break;

groupNext=kth.next;

// reverse group
varprev=kth.next;
varcurr=groupPrev.next;

while(curr!=groupNext)
{
vartemp=curr.next;
curr.next=prev;
prev=curr;
curr=temp;
}

vartmp=groupPrev.next;
groupPrev.next=kth;
groupPrev=tmp;
}

returndummy.next;
}

privateListNodegetKth(ListNodecurr,intk)
{
while(curr!=null&&k>0)
{
curr=curr.next;
k-=1;
}

returncurr;
}
}