[USACO12MAR]摩天大楼里的奶牛Cows in a Skyscraper

[USACO12MAR]摩天大楼里的奶牛Cows in a Skyscraper

题目描述

给出n个物品，体积为w[i]，现把其分成若干组，要求每组总体积<=W，问最小分组。(n<=18)

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
int n,w,a[20],f[300010],g[300010];
int read()
{
	int n=0,f=1;char c=getchar();
	while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}
	while(c>='0'&&c<='9'){n=n*10+c-'0';c=getchar();}
	return n*f;
}
int main()
{
	n=read(),w=read();
	for(int i=1;i<=n;++i)a[i]=read();
	memset(f,0x3f,sizeof(f));
	g[0]=w;
	f[0]=1;
	for(int i=0;i<(1<<n);++i)
		for(int j=1;j<=n;++j)
		{
			if(i&(1<<(j-1)))continue;
			if(g[i]>=a[j]&&f[i|(1<<(j-1))]>=f[i])
			{
				f[i|(1<<(j-1))]=f[i];
				g[i|(1<<(j-1))]=max(g[i]-a[j],g[i|(1<<(j-1))]);
			}
			if(g[i]<a[j]&&f[i|(1<<(j-1))]>=f[i]+1)
			{
				f[i|(1<<(j-1))]=f[i]+1;
				g[i|(1<<(j-1))]=max(w-a[j],g[i|(1<<(j-1))]);
			}
		}
	printf("%d",f[(1<<n)-1]);
	return 0;
}