[题目链接]

         https://codeforces.com/problemset/problem/140/C

[算法]

        显然 ， 我们每次应优先考虑数量多的雪球

        将雪球个数加入堆中 ， 每次取出数量前三大的雪球 ， 贪心地将它们分到一个组中即可

        时间复杂度 ： O(N log N)

[代码]

       

#include<bits/stdc++.h>
using namespace std;
const int MAXN = 1e5 + 10;

struct info
{
        int v1 , v2 , v3;
} ans[MAXN];

int n , tot;
int r[MAXN];
map< int,int > mp;
priority_queue< pair<int,int> > q;

template <typename T> inline void read(T &x)
{
    T f = 1; x = 0;
    char c = getchar();
    for (; !isdigit(c); c = getchar()) if (c == '-') f = -f;
    for (; isdigit(c); c = getchar()) x = (x << 3) + (x << 1) + c - '0';
    x *= f;
}

int main()
{
        
        read(n);
        for (int i = 1; i <= n; i++)
        {
                read(r[i]);
                mp[r[i]]++;
        }
        for (map< int,int > :: iterator it = mp.begin(); it != mp.end(); it++) q.push(make_pair(it -> second,it -> first));
        while ((int)q.size() >= 3)
        {
                pair<int,int> a = q.top();
                q.pop();
                pair<int,int> b = q.top();
                q.pop();
                pair<int,int> c = q.top();
                q.pop();
                ans[++tot] = (info){a.second,b.second,c.second};
                if (a.first > 1) q.push(make_pair(a.first - 1,a.second));
                if (b.first > 1) q.push(make_pair(b.first - 1,b.second));
                if (c.first > 1) q.push(make_pair(c.first - 1,c.second));
        }
        printf("%d\n",tot);
        for (int i = 1; i <= tot; i++) 
        {
                if (ans[i].v1 < ans[i].v2) swap(ans[i].v1,ans[i].v2);
                if (ans[i].v1 < ans[i].v3) swap(ans[i].v1,ans[i].v3);
                if (ans[i].v2 < ans[i].v3) swap(ans[i].v2,ans[i].v3);
                printf("%d %d %d\n",ans[i].v1,ans[i].v2,ans[i].v3);
        }
        
        return 0;
    
}