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=;
const int M=1e6+;
int a[N],n,bmin,bmax;
inline int read(){
    int x=,f=;char ch=getchar();
    while(!isdigit(ch)){if(ch=='-')f=-;ch=getchar();}
    while(isdigit(ch)){x=(x<<)+(x<<)+(ch^);ch=getchar();}
    return x*f;}
ll f[M];int ans;
int main(){
    scanf("%d%d%d",&n,&bmin,&bmax);
    rep(i,,n) a[i]=read();
    for(int i=;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 ;
}

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[],d[N],ans;
bool in[N];
queue<ll>que;

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