POJ 3417

树形DP+LCA

#include<cstdio>#include<cstring>#include<algorithm>#define N 100100using namespace std;int head1[N],head2[N],cnt,num;int dp[N],f[N];bool flag[N];struct Edge{    int v,next;}edge[N*4];void addedge(int u,int v,int *head){    edge[cnt].v=v;    edge[cnt].next=head[u];    head[u]=cnt++;    edge[cnt].v=u;    edge[cnt].next=head[v];    head[v]=cnt++;}void init(){    memset(head1,-1,sizeof(head1));    memset(head2,-1,sizeof(head2));    memset(flag,0,sizeof(flag));    memset(dp,0,sizeof(dp));    cnt=num=0;}int find(int u){    if(f[u]==u)return u;    return f[u]=find(f[u]);}void tarjan(int u,int fa){    int i;    f[u]=u;    for(i=head1[u];i!=-1;i=edge[i].next){        int v=edge[i].v;        if(v!=fa){            tarjan(v,u);            f[v]=u;        }    }    flag[u]=1;    for(i=head2[u];i!=-1;i=edge[i].next){        int v=edge[i].v;        if(flag[v]){            int t=find(v);            dp[u]++,dp[v]++,dp[t]-=2;        }    }}void DP(int u,int fa){    int i;    for(i=head1[u];i!=-1;i=edge[i].next){        int v=edge[i].v;        if(v!=fa){            DP(v,u);            dp[u]+=dp[v];        }    }}int main(){    int i,n,m;    int u,v;    scanf("%d %d",&n,&m);    init();    for(i=1;i<n;i++){        scanf("%d %d",&u,&v);        addedge(u,v,head1);    }    for(i=1;i<=m;i++){        scanf("%d %d",&u,&v);        addedge(u,v,head2);    }    tarjan(1,0);    DP(1,0);    int ans=0;    for(i=2;i<=n;i++){        if(dp[i]==0)ans+=m;        else if(dp[i]==1)ans++;    }    printf("%d\n",ans);    return 0;}