[luogu2329 SCOI2005] 栅栏(二分+搜索)

Posted 2021-01-10 menteur-hxy

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Solution

纯搜索80分，加二分90分，再补一个小剪枝满分qwq
真.小剪枝：如果下一个的需求和当前相同，那么不需要再次从头开始试(看代码就明白了233)

Code

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#define F(i,a,b) for(register int i=(a);i<=(b);i++)
using namespace std;

inline int read() {
    int x=0,f=1;char c=getchar();
    while(!isdigit(c)) {if(c=='-')f=-f;c=getchar();}
    while(isdigit(c)) x=(x<<1)+(x<<3)+c-48,c=getchar();
    return x*f;
}

const int M=55,N=1010;
int m,n,ans,tot;
int da[M],li[M],nd[N],s[N];

bool dfs(int las,int lef) {
    if(!las) return 1;
    F(i,lef,m) if(nd[las]<=da[i]) {
        da[i]-=nd[las];
        bool fla=dfs(las-1,nd[las]==nd[las-1]?i:1);
        da[i]+=nd[las];
        if(fla) return 1;
    }
    return 0;
}

int main() {
    m=read();F(i,1,m) da[i]=read(),tot+=da[i];
    n=read();F(i,1,n) nd[i]=read();
    sort(da+1,da+1+m);sort(nd+1,nd+1+n);
    F(i,1,n) s[i]=s[i-1]+nd[i];
    while(s[n]>tot) n--;
    int l=1,r=n;
    while(l<=r) {
        int mid=(l+r)>>1;
        if(dfs(mid,1)) ans=mid,l=mid+1;
        else r=mid-1;
    }
    printf("%d",ans);
    return 0;
}