CF788C The Great Mixing BFS+思维

这个模型十分巧妙啊，好题好题~

code:

#include <bits/stdc++.h>
#define N 3006
#define setIO(s) freopen(s".in","r",stdin)
using namespace std;
int n,k,vis[N],in[N],dp[N];
vector<int>v;
queue<int>q;
int main()
{
    int i,j;
    // setIO("input");
    scanf("%d%d",&n,&k);
    for(i=1;i<=k;++i)
    {
        int x;
        scanf("%d",&x), in[x]=1;
    }
    memset(dp,0x3f,sizeof(dp));
    for(i=0;i<=1000;++i)
    {
        if(in[i])
        {
            v.push_back(n-i);
            int x=n-i+1000;
            dp[x]=1;
            if(x==1000)
            {
               printf("1\n");
               return 0;
            }
            q.push(x);
        }
    }
    for(;!q.empty();)
    {
        int u=q.front();q.pop();
        for(i=0;i<v.size();++i)
        {
            int x=u+v[i];
            if(x>=0&&x<=2000&&dp[x]>dp[u]+1)
            {
                dp[x]=dp[u]+1;
                q.push(x);
            }
        }
    }
    if(dp[1000]>=100000) printf("-1\n");
    else printf("%d\n",dp[1000]);
    return 0;
}