UVa 11057 - Exact Sum

// UVa 11057 - Exact Sum

#include <iostream>
#include <string.h>
#include <stdio.h>
using namespace std;

#define mx 1000001
#define integer long long int

integer abs(integer x) {
	if (x < 0)
		return -x;
	else
		return x;
}

int c[mx + 1], b[mx + 1];
integer a[10000];

int main() {
	int n;
	while (cin >> n) {
		memset(c, 0, sizeof(c));
		for (int i = 0; i < n; i++) {
			cin >> a[i];
			if (a[i] <= mx) {
				c[a[i]]++;
				if (c[a[i]] == 1)
					b[a[i]] = i;
			}
		}
		integer m;
		int s;
		cin >> m;
		integer best_dif = m;
		for (int i = 0; i < n; i++) {
			integer o = m - a[i];
			if (o >= 0 && o <= mx && (c[o] > 1 || c[o] == 1 && b[o] != i)) {
				if (abs(a[i] - o) < best_dif) {
					best_dif = abs(a[i] - o);
					s = i;
				}
			}
		}
		printf("Peter should buy books whose prices are %lld and %lld.\n\n", min(a[s], m - a[s]), max(a[s], m - a[s]));
	}
	return 0;
}