poj 2393 Yogurt factory（贪心）

Yogurt factory

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.

代码：

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;

typedef long long LL;
LL dp[10010],num[10010];

int main()
{
LL n,s;
scanf("%I64d%I64d",&n,&s);
for(LL i=0; i<n; ++i)
scanf("%I64d%I64d",&dp[i],&num[i]);
for(LL i=1;i<n;++i)
dp[i]=min(dp[i-1]+s,dp[i]);
LL ans=0;
for(LL i=0; i<n; ++i)
ans+=dp[i]*num[i];
printf("%I64d\n",ans);
return 0;
}