【BZOJ】1082: [SCOI2005]栅栏（二分+dfs）

#include <cstdio>
#include <cstring>
#include <cmath>
#include <string>
#include <iostream>
#include <algorithm>
#include <queue>
#include <set>
#include <map>
using namespace std;
typedef long long ll;
#define rep(i, n) for(int i=0; i<(n); ++i)
#define for1(i,a,n) for(int i=(a);i<=(n);++i)
#define for2(i,a,n) for(int i=(a);i<(n);++i)
#define for3(i,a,n) for(int i=(a);i>=(n);--i)
#define for4(i,a,n) for(int i=(a);i>(n);--i)
#define CC(i,a) memset(i,a,sizeof(i))
#define read(a) a=getint()
#define print(a) printf("%d", a)
#define dbg(x) cout << (#x) << " = " << (x) << endl
#define error(x) (!(x)?puts("error"):0)
#define rdm(x, i) for(int i=ihead[x]; i; i=e[i].next)
inline const int getint() { int r=0, k=1; char c=getchar(); for(; c<‘0‘||c>‘9‘; c=getchar()) if(c==‘-‘) k=-1; for(; c>=‘0‘&&c<=‘9‘; c=getchar()) r=r*10+c-‘0‘; return k*r; }

const int N=2005;
int v[N], n, m, w[N], sum[N], c[N], tot, rest;

bool dfs(int dep, int last) {
	if(!dep) return true;
	if(rest+sum[dep]>tot) return false;
	for1(i, last, n) {
		if(c[i]>=w[dep]) {
			c[i]-=w[dep];
			if(c[i]<w[1]) rest+=c[i];
			if(w[dep]==w[dep-1]) { if(dfs(dep-1, i)) return true; }
			else if(dfs(dep-1, 1)) return true;
			if(c[i]<w[1]) rest-=c[i];
			c[i]+=w[dep];
		}
	}
	return false;
}
bool check(int d) {
	memcpy(c, v, sizeof(int)*(n+1));
	rest=0;
	return dfs(d, 1);
}
int main() {
	read(n);
	for1(i, 1, n) read(v[i]), tot+=v[i];
	sort(v+1, v+1+n);
	read(m);
	for1(i, 1, m) read(w[i]);
	sort(w+1, w+1+m);
	for1(i, 1, m) sum[i]=sum[i-1]+w[i];
	while(sum[m]>tot) --m;
	int l=0, r=m, mid;
	while(l<=r) {
		mid=(l+r)>>1;
		if(check(mid)) l=mid+1;
		else r=mid-1;
	}
	print(l-1);
	return 0;
}