[USACO12FEB]牛券Cow Coupons

嘟嘟嘟

这其实是一道贪心题，而不是dp。

首先我们贪心的取有优惠券中价值最小的，并把这些东西都放在优先队列里，然后看[k + 1, n]中，有些东西使用了优惠券减的价钱是否比[1, k]中用了优惠券的物品更划算，是的话就更新。

 #include<cstdio>
 #include<iostream>
 #include<cmath>
 #include<algorithm>
 #include<cstring>
 #include<cstdlib>
 #include<cctype>
 #include<vector>
 #include<stack>
 #include<queue>
 using namespace std;
 #define enter puts("")
 #define space putchar(' ')
 #define Mem(a, x) memset(a, x, sizeof(a))
 #define rg register
 typedef long long ll;
 typedef double db;
 const int INF = 0x3f3f3f3f;
 const db eps = 1e-;
 const int maxn = 5e4 + ;
 inline ll read()
 {
   ll ans = ;
   char ch = getchar(), last = ' ';
   while(!isdigit(ch)) {last = ch; ch = getchar();}
   while(isdigit(ch)) {ans = ans *  + ch - ''; ch = getchar();}
   if(last == '-') ans = -ans;
   return ans;
 }
 inline void write(ll x)
 {
   if(x < ) x = -x, putchar('-');
   if(x >= ) write(x / );
   putchar(x %  + '');
 }

 int n, k;
 ll m;
 struct Node
 {
   ll c, p;
 }t[maxn];

 bool cc(Node a, Node b) {return a.c < b.c;}
 bool cp(Node a, Node b) {return a.p < b.p;}

 priority_queue<ll, vector<ll>, greater<ll> > q;

 int solve()
 {
   sort(t + , t + n + , cc);
   ll sum = ;
   for(int i = ; i <= k; ++i)
     {
       sum += t[i].c;
       if(sum > m) return i - ;
       else if(i == n) return n;
       q.push(t[i].p - t[i].c);
     }
   sort(t + k + , t + n + , cp);
   int ans = k;
   for(int i = k + ; i <= n; ++i)
     {
       ll tp = q.empty() ? (ll)INF * (ll)INF : q.top();
       if(t[i].p - t[i].c > tp)
     {
       sum += tp + t[i].c;
       q.pop(); q.push(t[i].p - t[i].c);
     }
       else sum += t[i].p;
       if(sum > m) return ans;
       ans++;
     }
   return ans;
 }

 int main()
 {
   n = read(); k = read(); m = read();
   for(int i = ; i <= n; ++i) t[i].p = read(), t[i].c = read();
   write(solve());
   return ;
 }