Bzoj1606 [usaco2008 dec]hay for sale 购买干草

Posted by yjjr's blog on February 6, 2018

标签:背包DP

Description

    约翰遭受了重大的损失:蟑螂吃掉了他所有的干草,留下一群饥饿的牛.他乘着容量为C(1≤C≤50000)个单位的马车,去顿因家买一些干草.  顿因有H(1≤H≤5000)包干草,每一包都有它的体积Vi(l≤Vi≤C).约翰只能整包购买,

他最多可以运回多少体积的干草呢?

Input

    第1行输入C和H,之后H行一行输入一个Vi.

Output

 

    最多的可买干草体积.

Sample Input

7 3  //总体积为7,用3个物品来背包

2

6

5





The wagon holds 7 volumetric units; threebales are offered for sale with

volumes of 2, 6, and 5 units, respectively.



Sample Output

7  //最大可以背出来的体积



HINT

Buying the two smaller bales fills the wagon.

 

Code

#include<bits/stdc++.h>
#define LL long long
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define dep(i,a,b) for(int i=a;i>=b;i--)
#define mem(x,num) memset(x,num,sizeof x)
using namespace std;
inline LL read()
{
	LL f=1,x=0;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
	return x*f;
}
const int maxn=5e4+6;
int n,v,a[maxn],f[maxn];

int main()
{
	v=read(),n=read();
	rep(i,1,n)a[i]=read();
	f[0]=1;
	rep(i,1,n)
	    dep(j,v,a[i])
	        if(f[j-a[i]])f[j]=1;
	dep(j,v,0)
	    if(f[j]){cout<<j<<endl;return 0;} 
}



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