D. Merge Equals（from Educational Codeforces Round 42 (Rated for Div. 2)）

模拟题，运用强大的stl。

 #include <iostream>
 #include <map>
 #include <algorithm>
 #include <set>

 #define N 150005
 using namespace std;
 typedef long long Int;
 const int maxn = 1e9 + ;
 map<long long, set<int> > mapp;
 long long a[N];

 int main()
 {
     int n;
     cin >> n;
     int all = n;
     for (int i = ; i <= n; i++)
     {
         cin >> a[i];
         mapp[a[i]].insert(i);
     }
     for (map<long long, set<int> >::iterator i = mapp.begin(); i != mapp.end(); i++)
     {
         while (i->second.size() > )
         {
             set<int>::iterator op1 = i->second.begin(), op2;
             op2 = op1; op2++;
             all--;
             int t1 = *op1, t2 = *op2;
             a[t1] = -;
             a[t2] *= ;
             mapp[a[t2]].insert(t2);
             i->second.erase(op1);
             i->second.erase(op2);
         }
     }
     cout << all << endl;
     for (int i = ; i <= n; i++)
     {
         if (a[i] != -)
             cout << a[i] << " ";
     }

     //system("pause");
     return ;
 }