5-19 求链式线性表的倒数第K项 (20分)

#include "vector"
#include "set"
#include "algorithm"
#include "iostream"
using namespace std;
vector<int> Q1;
int main( )
{
vector<int>::iterator A;

int m,k;
scanf("%d" , &k) ;
while(1)
{
scanf("%d" , &m);
if(m<0) break;
Q1.push_back(m);
}

if(k<0 || k>Q1.size()) cout<<"NULL"<<endl;

else
{
A=Q1.end();

cout<<*(A-k)<<endl;
}

return 0;
}