CodeForces #100 C 贪心+STL

#include <stdio.h>
#include <iostream>
#include <set>
#include <map>
#include <vector>
#include <algorithm>
using namespace std;

typedef pair<int, int> pair_;
map<int, int> mp;
set<pair_> st;
vector<int> ans;

int main() {
    //freopen("in.cpp", "r", stdin);
    int n;
    while(~scanf("%d", &n)) {
       mp.clear();
       st.clear();
       ans.clear();
       int temp;
       for (int i=0; i<n; ++i) {
            scanf("%d", &temp);
            mp[temp]++;
       }
       map<int, int>::iterator mpit;
       for (mpit = mp.begin(); mpit != mp.end(); ++mpit) {
            //st.insert(pair_((*mpit).second, (*mpit).first));
            st.insert(pair_(mpit->second, mpit->first));
       }
       while(st.size() >= 3) {
        pair_ now[3];
        for (int i=0; i<3; ++i) {
            now[i] = *--st.end();
            st.erase(--st.end());
            ans.push_back(now[i].second);
        }
        for (int i=0; i<3; ++i) {
            if (--now[i].first) st.insert(now[i]);
        }
        sort(ans.rbegin(),ans.rbegin()+3);
       }
       printf("%d\n", ans.size()/3);
       for (int i=0; i<ans.size(); i+=3) {
        printf("%d %d %d\n", ans[i], ans[i+1], ans[i+2]);
       }
    }
    return 0;
}