POJ2393 Yogurt factory(贪心)

题目：

Yogurt factory Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 10782   Accepted: 5469 Description The cows have purchased a yogurt factory that makes world-famous Yucky Yogurt. Over the next N (1 <= N <= 10,000) weeks, the price of milk and labor will fluctuate weekly such that it will cost the company C_i (1 <= C_i <= 5,000) cents to produce one unit of yogurt in week i. Yucky's factory, being well-designed, can produce arbitrarily many units of yogurt each week.  Yucky Yogurt owns a warehouse that can store unused yogurt at a constant fee of S (1 <= S <= 100) cents per unit of yogurt per week. Fortuitously, yogurt does not spoil. Yucky Yogurt's warehouse is enormous, so it can hold arbitrarily many units of yogurt.  Yucky wants to find a way to make weekly deliveries of Y_i (0 <= Y_i <= 10,000) units of yogurt to its clientele (Y_i is the delivery quantity in week i). Help Yucky minimize its costs over the entire N-week period. Yogurt produced in week i, as well as any yogurt already in storage, can be used to meet Yucky's demand for that week. Input * Line 1: Two space-separated integers, N and S.  * Lines 2..N+1: Line i+1 contains two space-separated integers: C_i and Y_i. Output * Line 1: Line 1 contains a single integer: the minimum total cost to satisfy the yogurt schedule. Note that the total might be too large for a 32-bit integer. Sample Input 4 5 88 200 89 400 97 300 91 500 Sample Output 126900 Hint OUTPUT DETAILS:  In week 1, produce 200 units of yogurt and deliver all of it. In week 2, produce 700 units: deliver 400 units while storing 300 units. In week 3, deliver the 300 units that were stored. In week 4, produce and deliver 500 units.  Source USACO 2005 March Gold

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思路：

有一个奶牛场，他要向客户供奶，一共要n周，但是生产牛奶的单位价格每一周都不一样，他有一个仓库，可以保存牛奶而且永不过期，每保存一周有固定的保存费用s，现在给出n周的每周生产单位牛奶的价格和每周要和客户供奶的量，求最小花费是多少

我们可以用贪心的思想，维护一个c=min(c,minc+s)来看一下这一周是保存牛奶比较好还是直接生产比较好，具体看代码

代码：

#include<cstdio>
#include<cstring>
#include<string>
#include<set>
#include<iostream>
#include <cmath>
#include<stack>
#include<queue>
#include<vector>
#include<algorithm>
#define mem(a,b) memset(a,b,sizeof(a))
#define inf 0x3f3f3f3f
#define mod 10000007
#define debug() puts("what the fuck!!!")
#define N (1010)
#define ll long long
using namespace std;
int main()
{
    ll n,s,minc = inf;
    scanf("%lld%lld",&n, &s);
    ll sum = 0;
    while(n --)
    {
        ll c, y;
        scanf("%lld%lld",&c, &y);
        c=min(c,minc+s);
        minc = c;
        sum +=c*y;
    }
    printf("%lld\n", sum);
    return 0;
}