HDU 1520 tree DP

Analysis: although we can see that there is a directed edge, we can do it with a undirected edge!

 

#include<iostream>  #include<cstdio>  #include<cstring>   using namespace std; const int maxn=6010;  struct node{     int v;     node *next; }tree[maxn<<1],*head[maxn];  int n,ptr; bool vis[maxn]; int dp[maxn][2],val[maxn];  void Init(){     ptr=1;     memset(vis,false,sizeof(vis));     memset(dp,0,sizeof(dp));     memset(head,0,sizeof(head)); }  void AddEdge(int x,int y){     tree[ptr].v=y;     tree[ptr].next=head[x];     head[x]=&tree[ptr++]; }  void DFS(int cnt){     vis[cnt]=true;     dp[cnt][1]=val[cnt];     node *p=head[cnt];     while(p!=NULL){         if(vis[p->v]){             p=p->next; continue;         }         DFS(p->v);         dp[cnt][1] += dp[p->v][0];         dp[cnt][0] += max(dp[p->v][1], dp[p->v][0]);         p=p->next;     } }  int main(){     while(~scanf("%d",&n)&&n){         Init();         for(int i=1;i<=n;++i)             scanf("%d",val+i);         int a,b;         while(scanf("%d%d",&a,&b)&&a+b){             AddEdge(a,b);             AddEdge(b,a);         }         DFS(1);         printf("%d\n",max(dp[1][0],dp[1][1]));     }     return 0; }