Hdu 2242 (dual Unicom + tree DP)

After the Tarjan double-link deflation point, you can choose one of them as the root node to find the number of byte points of all points + 1: m

Then the difference between n-m and m is obtained, and the minimum value is obtained.

 

 

 

 

#include<stdio.h>#include<stack>#include<string.h>#define inf 0x3fffffff#define N 10001using namespace std;int belong[N],dfs[N],low[N],idx,ans,head[N],num,n,m,people[N],pe[N],nume,sum,vis[N];struct edge{int st,ed,next;}E[N*4],e[N*4];void addedge(int x,int y){E[num].st=x;E[num].ed=y;E[num].next=head[x];head[x]=num++;}void Addedge(int x,int y){e[nume].st=x;e[nume].ed=y;e[nume].next=head[x];head[x]=nume++;}stack<int>Q;void Tarjan(int u,int father){    int i,j,v,flag=0;low[u]=dfs[u]=idx++;Q.push(u);for(i=head[u];i!=-1;i=E[i].next){v=E[i].ed;if(dfs[v]==-1){Tarjan(v,u);low[u]=low[u]>low[v]?low[v]:low[u];}else if(v==father){if(flag)low[u]=low[u]>dfs[v]?dfs[v]:low[u];flag++;}else low[u]=low[u]>dfs[v]?dfs[v]:low[u];}if(dfs[u]==low[u]){do{j=Q.top();Q.pop();belong[j]=ans;people[ans]+=pe[j];}while(j!=u);ans++;}}void buildmap(){memset(head,-1,sizeof(head));nume=0;for(int i=0;i<num;i+=2){       int x=belong[E[i].st];   int y=belong[E[i].ed];   if(x==y)continue;   Addedge(x,y);   Addedge(y,x);}}int mn;int discost(int u){int cont=people[u];vis[u]=1;for(int i=head[u];i!=-1;i=e[i].next){int v=e[i].ed;if(vis[v]==1)continue;int temp=discost(v);cont+=temp;temp=sum-2*temp;if(temp<0)temp=-temp;if(mn>temp)mn=temp;}return cont;}int main(){int i,x,y;while(scanf("%d%d",&n,&m)!=-1){sum=0;memset(head,-1,sizeof(head));num=0;for(i=0;i<n;i++){scanf("%d",&pe[i]);sum+=pe[i];}for(i=0;i<m;i++){scanf("%d%d",&x,&y);addedge(x,y);addedge(y,x);}idx=ans=0;memset(dfs,-1,sizeof(dfs));memset(people,0,sizeof(people));Tarjan(0,-1);if(ans==1)        {            printf("impossible\n");            continue;        }buildmap();memset(vis,0,sizeof(vis));mn=inf;discost(0);printf("%d\n",mn);}return 0;}