11057

#include <iostream>
#include <cstdlib>
#include <cstdio>

#define SZ 10005
#define INF 100000000
#define ll  long long

using namespace std;

ll a[SZ];

int main()
{
	ll N,M,MN;
	bool f=0;
	ll price2,price1;

	price2 = 1000001;
	price1 = 1000001;

	int d = price1+price2;
	//cout<<d<<"\n";

	while(cin>>N)
	{
		MN = INF;
		for(int i=0;i<N;i++)
			cin>>a[i];
		cin>>M;
		for(int i=0;i<N;i++)
		{
			for(int j=0;j<N;j++)
			{
				if(a[i]+a[j]==M && i!=j)
				{
					if(abs(a[i]-a[j])<MN)
					{
						MN = abs(a[i]-a[j]);
						price1 = a[i];
						price2 = a[j];
					}
				}
			}
		}//for loop

		if(price1>price2)
		{
			price1 = price1 + price2;
			price2 = price1 - price2;
			price1 = price1 - price2;
		}
		cout<<"Peter should buy books whose prices are "<<price1<<" and "<<price2<<".\n\n";
	}//while
}

Another way:

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>

#define INF 10000000

using namespace std;

bool val[1000005];
int arr[10005];

int main()
{
	int N,tmp,d;
	int total,diff;
	int I,J;
	while(scanf("%d",&N)!=EOF)
	{
		memset(arr,0,sizeof(arr));
		memset(val,0,sizeof(val));
		diff=INF;
		for(int i=0;i<N;i++)
		{
			cin>>arr[i];
			val[arr[i]]=1;
		}
		cin>>total;

		for(int i=0;i<N;i++)
		{
			tmp=total-arr[i];
			if(tmp<0)
			continue;
			if(tmp>1000001)
			continue;
			if(val[tmp])
			{
				d = abs(arr[i]-tmp);
				if(d<diff)
				{
					diff=d;
					I=arr[i];
					J=tmp;
				}
			}
		}
		if(I>J)
		{
			I=I+J;
			J=I-J;
			I=I-J;
		}
		cout<<"Peter should buy books whose prices are "<<I<<" and "<<J<<".\n\n";
	}
	return 0;
}