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

/**
 * Definition for singly-linked list.
 * class ListNode {
 * val: number
 * next: ListNode | null
 * constructor(val?: number, next?: ListNode | null) {
 * this.val = (val===undefined ? 0 : val)
 * this.next = (next===undefined ? null : next)
 * }
 * }
 */

functionreverseKGroup(head: ListNode|null,k: number): ListNode|null{
letdummy=newListNode(0,head);
letgroupPrev=dummy;

while(true){
letkth=getKth(groupPrev,k);
if(!kth){
break;
}

letgroupNext=kth.next;

// reverse group
letprev=kth.next;
letcurr=groupPrev.next;

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

lettemp=groupPrev.next;
groupPrev.next=kth;
groupPrev=temp;
}

returndummy.next;
}

functiongetKth(curr: ListNode|null,k: number): ListNode|null{
while(curr&&k>0){
curr=curr.next;
k-=1;
}

returncurr;
}