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最新推荐文章于 2021-01-14 16:55:55 发布

原创最新推荐文章于 2021-01-14 16:55:55 发布 · 332 阅读

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#include<stdio.h>
#include<string.h>
#include<stack>
#include<string>
#include<math.h>
#include<queue>
#include<set>
#include<algorithm>
#include<iostream>
#include<vector>
#include<map>
using namespace std;
#define LL __int64
#define inf 1999999999
#define N 10010
#define mod 1000000007
int low[N],dfn[N],vis[N],belong[N],a[N],aa[N];
vector<int>edge1[N],edge2[N];
stack<int>s;
int cnt,n,m,Index,ans,sum;
void init()
{
    memset(low,0,sizeof(low));
    memset(dfn,0,sizeof(dfn));
    memset(vis,0,sizeof(vis));
    memset(belong,0,sizeof(belong));
    memset(aa,0,sizeof(aa));
    for(int i=1;i<=n;i++)
    {
        edge1[i].clear();
        edge2[i].clear();
    }
    while(!s.empty()) s.pop();
    Index=cnt=sum=0; ans=inf;
}
void tarjan(int u,int pre)
{
    int i,v;
    low[u]=dfn[u]=++Index;
    vis[u]=1;s.push(u);
    int flag=0;
    for(i=0;i<edge1[u].size();i++)
    {
        v=edge1[u][i];
        if(v==pre&&!flag)
        {
            flag=1;continue;
        }
        if(!dfn[v])
        {
            tarjan(v,u);
            low[u]=min(low[u],low[v]);
        }
        else if(vis[v])
            low[u]=min(low[u],dfn[v]);
    }
    if(dfn[u]==low[u])
    {
        cnt++;
        do
        {
            v=s.top();s.pop();
            belong[v]=cnt;
            vis[v]=0;
            aa[cnt]+=a[v];
        }while(v!=u);
    }
}
int dfs(int u,int pre)
{
    int res=aa[u];
    for(int i=0;i<edge2[u].size();i++)
    {
        int v=edge2[u][i];
        if(v==pre) continue;
        res+=dfs(v,u);
    }
    ans=min(ans,abs(sum-res-res));
    return res;
}
int main()
{
    int i,j,u,v;
    while(scanf("%d%d",&n,&m)!=-1)
    {
        init();
        for(i=1;i<=n;i++)
        {
            scanf("%d",&a[i]);
            sum+=a[i];
        }
        for(i=1;i<=m;i++)
        {
            scanf("%d%d",&u,&v);
            u++;v++;
            edge1[u].push_back(v);
            edge1[v].push_back(u);
        }
        for(i=1;i<=n;i++)
        {
            if(!dfn[i])
                tarjan(i,i);
        }
        if(cnt==1) {printf("impossible\n");continue;}
        for(i=1;i<=n;i++)
        {
            for(j=0;j<edge1[i].size();j++)
            {
                u=i;v=edge1[i][j];
                if(belong[u]!=belong[v])
                    edge2[belong[u]].push_back(belong[v]);
            }
        }
        dfs(1,1);
        printf("%d\n",ans);
    }
    return 0;
}