410 - Station Balance, uva, solution

#include<iostream>
#include<cstdio>
#include<utility>
#include<cmath>
#include<cstring>
#include<vector>
#include<algorithm>
#define db(a) cout << #a << " = " << a << endl
using namespace std;
bool cmp(const pair<int, int>& a, const pair<int, int>& b) {
 return a.first <= b.first;
}
bool cmp_list(const vector< pair<int, int> >& a, const vector< pair<int, int> >& b) {
 int min_a = 20, min_b = 20;
 for (int i = 0; i < a.size(); i++) {
  if (a[i].second < min_a) min_a = a[i].second;
 }
 for (int i = 0; i < b.size(); i++) {
  if (b[i].second < min_b) min_b = b[i].second;
 }
 return min_a <= min_b;
}
int main() {
 int c, s, cont = 0;
 #ifdef dennisbot
  freopen("in.in", "r", stdin);
  freopen("ou.out", "w", stdout);
 #endif
 while (scanf("%d %d", &c, &s) !=EOF) {
  vector< pair<int, int> > lista(2 * c);
  double A = 0;
  for (int i = 0; i < s; i++) {
   scanf("%d", &lista[i].first);   
   A += lista[i].first;
   lista[i].second = i;
  }
  for (int i = s; i < 2 * c; i++) {
   lista[i].second  = i;
  }
  A /= c;
  
  sort(lista.begin(), lista.end(), cmp);
  
  double res = 0;
  vector< vector< pair<int, int> > > elementos(c);
  for (int i = 0; i < c; i++) {
   res += fabs(lista[i].first + lista[2 * c - i - 1].first - A); 
   if (lista[i].second < lista[2 * c - i - 1].second) {
    elementos[i].push_back(lista[i]);
    elementos[i].push_back(lista[2 * c - i - 1]);
   }
   else {
    elementos[i].push_back(lista[2 * c - i - 1]);
    elementos[i].push_back(lista[i]);
   }
  }
  printf("Set #%d\n", ++cont);
  int n = elementos.size();
  
  sort(elementos.begin(), elementos.end(), cmp_list);
  for (int i = 0; i  < c; i++) {
    printf("% d:", i);
    for (int j = 0; j < elementos[i].size(); j++) {
     if (elementos[i][j].first != 0)
     printf(" %d", elementos[i][j].first);
    }
    puts("");
  }
  printf("IMBALANCE = %.5f\n\n", res);
 }
 return 0;
}