7-19 求链式线性表的倒数第K项 (20分)

不知道题目说的尽可能高效的算法是啥，我就只按我会的来了，无语……

有时候最后两个测试点会超时，再提交一次又能AC了。

#include <iostream>
#include <string>
#include <cstring>
using namespace std;

struct node
{
    int data;
    struct node* next;
};

typedef struct node* node_ptr;
int null_flag = 0;

int main()
{
    int K;
        cin >> K;
        node_ptr p_end = NULL;
        int temp;
        while(1)
        {
            cin >> temp;
            if (temp < 0)
            {
                break;
            }
            else
            {
                node_ptr s = new struct node;
                s->data = temp;
                s->next = p_end;
                p_end = s;
            }
        }
        int t = 1;
        node_ptr ptemp = p_end;
        while (t++ < K)
        {
            if (NULL != ptemp->next)
            {
                ptemp = ptemp->next;
                continue;
            }
            else
            {
                break;
            }
        }
        if (t == K + 1)
            cout << ptemp->data << endl;
        else
            cout << "NULL";
    return 0;
}