25. Reverse Nodes in k-Group（js）

25. Reverse Nodes in k-Group

Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.

k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes in the end should remain as it is.

Example:

Given this linked list: 1->2->3->4->5

For k = 2, you should return: 2->1->4->3->5

For k = 3, you should return: 3->2->1->4->5

Note:

• Only constant extra memory is allowed.
• You may not alter the values in the list's nodes, only nodes itself may be changed.

题意：对给定链表每k个节点进行反转一次

代码如下：

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} k
 * @return {ListNode}
 */
var reverseKGroup = function(head, k) {
    if(!head || k===1) return head;
    var dummy=new ListNode(-1);
    var pre=dummy,cur=head;
    dummy.next=head;
    var i=0;
    while(cur){
        i++;
        if(i%k===0){
            pre=reverseOneGroup(pre,cur.next);
            cur=pre.next;
        }else{
            cur=cur.next;
        }
    }
    return dummy.next;
};
var reverseOneGroup=function(pre,next){
    var last=pre.next;
    var cur=last.next;
    while(cur!==next){
        last.next=cur.next;
        cur.next=pre.next;
        pre.next=cur;
        cur=last.next;
    }
    return last;
}