【BZOJ1082】[SCOI2005]栅栏（搜索）
题面
题解
随便写个爆搜，洛谷上就(80)分了。先放爆搜代码：
#include<iostream>
#include<cstdio>
using namespace std;
inline int read()
{
int x=0;bool t=false;char ch=getchar();
while((ch<'0'||ch>'9')&&ch!='-')ch=getchar();
if(ch=='-')t=true,ch=getchar();
while(ch<='9'&&ch>='0')x=x*10+ch-48,ch=getchar();
return t?-x:x;
}
int n,m,a[55],b[1010],l[55],ans;
void dfs(int x,int s)
{
if(s+n-x+1<=ans)return;
if(x==n+1){ans=s;return;}
dfs(x+1,s);
for(int i=1;i<=m;++i)
if(l[i]+b[x]<=a[i])
l[i]+=b[x],dfs(x+1,s+1),l[i]-=b[x];
}
int main()
{
m=read();
for(int i=1;i<=m;++i)a[i]=read();
n=read();
for(int i=1;i<=n;++i)b[i]=read();
dfs(1,0);
printf("%d
",ans);
}
然后发现可以二分，二分之后再玄学剪枝就好了。
#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
inline int read()
{
int x=0;bool t=false;char ch=getchar();
while((ch<'0'||ch>'9')&&ch!='-')ch=getchar();
if(ch=='-')t=true,ch=getchar();
while(ch<='9'&&ch>='0')x=x*10+ch-48,ch=getchar();
return t?-x:x;
}
int n,m,a[55],b[1010],sum,tot,s[1010];
bool dfs(int x,int lst)
{
if(!x)return true;
if(sum+s[x]>tot)return false;
for(int i=lst;i<=m;++i)
if(b[x]<=a[i])
{
a[i]-=b[x];if(a[i]<b[1])sum+=a[i];
bool fl=dfs(x-1,b[x]==b[x-1]?i:1);
if(a[i]<b[1])sum-=a[i];a[i]+=b[x];
if(fl)return true;
}
return false;
}
int main()
{
m=read();for(int i=1;i<=m;++i)tot+=(a[i]=read());
n=read();for(int i=1;i<=n;++i)b[i]=read();
sort(&a[1],&a[m+1]);sort(&b[1],&b[n+1]);
for(int i=1;i<=n;++i)s[i]=s[i-1]+b[i];
while(s[n]>tot)--n;
int l=0,r=n,ret=0;
while(l<=r)
{
int mid=(l+r)>>1;
if(dfs(mid,1))l=mid+1,ret=mid;
else r=mid-1;
}
printf("%d
",ret);return 0;
}