CoderForce 140C-New Year Snowmen(贪心)

题目大意：有n个已知半径的雪球。堆一个雪人需要三个尺寸不同的雪球，问用这些雪球最多能堆多少个雪人？

题目分析：先统计一下每种尺寸的球的个数，从三种最多的种类中各取出一个堆成雪人，这样贪心能保证的到的数目最多。

代码如下：

# include<iostream>
# include<map>
# include<vector>
# include<cstdio>
# include<queue>
# include<algorithm>
using namespace std;

struct Node
{
    int val,cnt;
    Node(int _val,int _cnt):val(_val),cnt(_cnt){}
    bool operator < (const Node &a) const{
        return cnt<a.cnt;
    }
};
int ans[40005][3],n;
map<int,int>mp;
priority_queue<Node>q;

void solve()
{
    int cnt=0;
    while(!q.empty()){
        Node a=q.top();
        q.pop();
        if(q.empty()) break;
        Node b=q.top();
        q.pop();
        if(q.empty()) break;
        Node c=q.top();
        q.pop();
        ans[cnt][0]=a.val;
        ans[cnt][1]=b.val;
        ans[cnt][2]=c.val;
        ++cnt;
        if(a.cnt-1>0) q.push(Node(a.val,a.cnt-1));
        if(b.cnt-1>0) q.push(Node(b.val,b.cnt-1));
        if(c.cnt-1>0) q.push(Node(c.val,c.cnt-1));
    }
    printf("%d
",cnt);
    for(int i=0;i<cnt;++i){
        sort(ans[i],ans[i]+3);
        printf("%d %d %d
",ans[i][2],ans[i][1],ans[i][0]);
    }
}

int main()
{
    int a;
    while(~scanf("%d",&n))
    {
        mp.clear();
        for(int i=0;i<n;++i){
            scanf("%d",&a);
            ++mp[a];
        }
        map<int,int>::iterator it;
        while(!q.empty()) q.pop();
        for(it=mp.begin();it!=mp.end();++it){
            q.push(Node(it->first,it->second));
        }
        solve();
    }
    return 0;
}