luogu 2371 墨墨的等式

1.背包dp

#include<bits/stdc++.h>
#define rep(i,x,y) for(register int i=x;i<=y;i++)
#define ll long long 
using namespace std;
const int N=20;
const int M=1e6+50;
int a[N],n,bmin,bmax;
inline int read(){
    int x=0,f=1;char ch=getchar();
    while(!isdigit(ch)){if(ch=='-')f=-1;ch=getchar();}
    while(isdigit(ch)){x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}
    return x*f;}
ll f[M];int ans;
int main(){
    scanf("%d%d%d",&n,&bmin,&bmax);
    rep(i,1,n) a[i]=read();
    for(int i=1;i<=n;i++)
    for(int j=a[i];j<=bmax;j++)
    f[j]=max(f[j],f[j-a[i]]+a[i]);
    
    for(int i=bmin;i<=bmax;i++)if(f[i]==i) ++ans;
    printf("%d\n",ans);return 0; 
}

2.最短路  啊啊啊搬了别人的代码，以后自己再写吧

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<queue>
#include<cstring>
#define ll long long
#define INF 0x3f3f3f3f3f3f3f3f
#define N 500100
using namespace std;

ll n,l,r,num[20],d[N],ans;
bool in[N];
queue<ll>que;

int main()
{
    ll i,j,p,q;
    cin>>n>>l>>r;
    for(i=1; i<=n; i++)
    {
        scanf("%lld",&num[i]);
    }
    sort(num+1,num+n+1);
    memset(d,0x3f,sizeof(d));
    d[0]=0;
    que.push(0);
    for(; !que.empty();)
    {
        p=que.front();
        que.pop();
        in[p]=0;
        for(i=2; i<=n; i++)
        {
            q=(p+num[i])%num[1];
            if(d[q]<=d[p]+num[i]) continue;
            d[q]=d[p]+num[i];
            if(!in[q])
            {
                in[q]=1;
                que.push(q);
            }
        }
    }
    for(i=0,l--; i<num[1]; i++)
    {
        if(d[i]>r) continue;
        if(d[i]<=l) ans+=(r-i)/num[1]-(l-i)/num[1];
        else ans+=(r-d[i])/num[1]+1;
    }
    cout<<ans;
}