js 之k个一组翻转链表

题目描述

将给出的链表中的节点每\ k k 个一组翻转，返回翻转后的链表
如果链表中的节点数不是\ k k 的倍数，将最后剩下的节点保持原样
你不能更改节点中的值，只能更改节点本身。
要求空间复杂度 \ O(1) O(1)

 

例如：

给定的链表是  1→2→3→4→5

对于 k = 2 , 你应该返回   2→1→4→3→5

对于 k = 3, 你应该返回 3→2→1→4→5

 

代码：

/*
 * function ListNode(x){
 *   this.val = x;
 *   this.next = null;
 * }
 */

/**
  *
  * @param head ListNode类
  * @param k int整型
  * @return ListNode类
  */
//js翻转链表算法
function myReverse(head, tail){
    let pre = null;
    let cur = head;
//     const nex = cur.next;
    let nex = null;
    while(pre != tail){
        nex = cur.next;
        cur.next = pre;
        pre = cur;
        cur = nex;
    }
    return [tail, head];
}

function reverseKGroup( head ,  k ) {
    const hair = new ListNode(0);
    hair.next = head;
    let pre = hair;

    while(head){
        let tail = pre;

        //查看剩余部分长度的hi否大于等于K
        for(let i =0; i < k; i++){
            tail = tail.next;
            if(!tail){
                return hair.next;
            }
        }

        const cur = tail.next;
        [head, tail] = myReverse(head, tail);
        pre.next = head;
        tail.next = cur;
        pre = tail;
        head = tail.next;
    }
    return hair.next;
    // write code here
}
module.exports = {
    reverseKGroup : reverseKGroup
};

　C语言版本的代码：

/*
 * function ListNode(x){
 *   this.val = x;
 *   this.next = null;
 * }
 */

/**
  *
  * @param head ListNode类
  * @param k int整型
  * @return ListNode类
  */
function reverseKGroup( head ,  k ) {
    // write code here
    var dummy = new ListNode(-1);
    dummy.next = head;
    var pre=dummy,start=head,end=head,low=head;
    while(!low){
        for(let i=1;i<k && end!==null;i++ ){
            end = end.next
        }
        if(end === null){
            break;
        }
        //low指针已经走了k步
        low = end.next;
        end.next = null;
        end = start;
        start = reverse(start);

        //翻转链表之后调整首尾
        end.next = low;
        pre.next = start;
        //重新指定pre start end
        pre = end;
        start = low;
        end = start;
    }
    return dummy.next;
}
//翻转链表
function reverse(head){
     var pre = null,low = null
     var cur = head;
    while(!cur){
        low = cur.next;
        cur.next = pre;
        pre = cur;
        cur = low;
    }
    //返回翻转后的链表头结点
    return pre;
}

module.exports = {
    reverseKGroup : reverseKGroup
};