【贪心+Treap】BZOJ1691-[Usaco2007 Dec]挑剔的美食家

【题目大意】

有n头奶牛m种牧草，每种牧草有它的价格和鲜嫩度。每头奶牛要求它的牧草的鲜嫩度要不低于一个值，价格也不低于一个值。每种牧草只会被一头牛选择。问最少要多少钱？

【思路】

显然的贪心，把奶牛和牧草都按照鲜嫩度由大到小排序，对于每奶牛把鲜嫩度大于它的都扔进treap，然后找出后继。

不过注意后继的概念是大于它且最小的，然而我们这里是可以等于的，所以应该是找cow[i].fresh-1的后继，注意一下……

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<cmath>
 using namespace std;
 typedef long long ll;
 const int MAXN=+;
 const int INF=0x7fffffff;
 struct node
 {
     int fresh,price;
     bool operator < (const node &x) const
     {
         return (fresh>x.fresh);//注意是由大到小排序
     }
 }cow[MAXN],grass[MAXN];
 struct treap
 {
     int key,cnt,priority;
     treap* lson;
     treap* rson;
     treap()
     {
         cnt=;
         priority=rand();
         lson=rson=NULL;
     }
 };
 treap* root=NULL;
 int n,m;

 void RightRotate(treap* &rt)
 {
     treap* tmp=rt->lson;
     rt->lson=tmp->rson;
     tmp->rson=rt;
     rt=tmp;
 }

 void LeftRotate(treap* &rt)
 {
     treap* tmp=rt->rson;
     rt->rson=tmp->lson;
     tmp->lson=rt;
     rt=tmp;
 }

 void insert(treap* &rt,int x)
 {
     if (rt==NULL)
     {
         rt=new treap;//不要忘记了新建
         rt->key=x;
     }
     else if (rt->key==x) rt->cnt++;
     else
     {
         if (rt->key>x)
         {
             insert(rt->lson,x);
             if (rt->lson->priority>rt->priority) RightRotate(rt);
         }
         if (rt->key<x)
         {
             insert(rt->rson,x);
             if (rt->rson->priority>rt->priority) LeftRotate(rt);
         }
     }
 }

 void del(treap* &rt,int x)
 {
     if (rt->key==x)
     {
         if (rt->cnt>) rt->cnt--;
             else
             {
                 treap* tmp=rt;
                 if (rt->lson==NULL)
                 {
                     rt=rt->rson;
                     delete tmp;
                 }
                 else if (rt->rson==NULL)
                 {
                     rt=rt->lson;
                     delete tmp;
                 }
                 else
                 {
                     if (rt->lson->priority>rt->rson->priority) RightRotate(rt),del(rt->rson,x);
                         else LeftRotate(rt),del(rt->lson,x);
                 }
             }
     }
     else
     {
         if (x<rt->key) del(rt->lson,x);
             else del(rt->rson,x);
     }
 }

 int suc(treap* &rt,int x)
 {
     int ans=INF;
     treap* tmp=rt;
     while (tmp)
     {
         if (tmp->key>x)
         {
             ans=min(ans,tmp->key);
             tmp=tmp->lson;
         }
         else tmp=tmp->rson;
     }
     return ans;
 }

 void init()
 {
     scanf("%d%d",&n,&m);
     for (int i=;i<=n;i++) scanf("%d%d",&cow[i].price,&cow[i].fresh);
     for (int i=;i<=m;i++) scanf("%d%d",&grass[i].price,&grass[i].fresh);
     sort(cow+,cow+n+);
     sort(grass+,grass+m+);
 }

 ll solve()
 {
     int j=;
     ll ans=;
     for (int i=;i<=n;i++)
     {
         while (grass[j].fresh>=cow[i].fresh && j<=m)
         {
             insert(root,grass[j].price);//这里一开始把j打成i了
             j++;
         }
         int find=suc(root,cow[i].price-);//注意由于这里是不低于，也就是≥，并不是取cow[i].price的后继，而是cow[i].price-1的
         if (find==INF) return(-);
             else
             {
                 ans+=(ll)find;
                 del(root,find);
             }
     }
     return ans;
 }

 int main()
 {
     init();
     printf("%lld",solve());
     return ;
 }