求链式线性表的倒数第K项

给定一系列正整数，请设计一个尽可能高效的算法，查找倒数第K个位置上的数字

//有部分测试未通过
#include <iostream>
using namespace std;
long int a[1000005];

typedef struct Node
{
    int data = 0;
    struct Node* next = NULL;
}Mylist;

void search(Mylist* node, int k)
{
    int i=0,j=1;
    Mylist* list1 = node;                  //为临时节点赋值
    Mylist* list2 = node;
    list1 = list1->next;
    while (0 <= (list1->data))              //判断
    {
        list1 = list1->next;              
        j = j + 1;
    }
    if (j < k)
    {
        cout << NULL;
    }
    else 
    {
        list2 = list2->next;
        for (i = 0; i <= (j-k-2);i++)
        {
            list2 = list2->next;
        }
        cout << list2->data;
    }
}

int main()
{
    int k = 0, i = 0, j = 0;
    cin >> k;
    Mylist* head,*p;
    head = new Mylist;
    p = head;
    for(i=0;i<1000005;i++)
    {
        cin >> a[i];
        if (a[i] < 0)
            break;
    }
    for (j = 0; j <= i; j++)
    {
        Mylist* newlist = new Mylist;      //创建新节点
        newlist->data = a[j];              //为新节点赋值
        head->next = newlist;              //老节点接新节点
        head = newlist;                  //更新节点以便下次遍历
    }
    search(p,k);
    return 0;
}