poj 2342树形dp板子题1

http://poj.org/problem?id=2342

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#include<vector>
using namespace std;
inline int read(){
    int sum=,x=;
    char ch=getchar();
    while(ch<''||ch>''){
        if(ch=='-')
            x=;
        ch=getchar();
    }
    while(ch>=''&&ch<=''){
        sum=(sum<<)+(sum<<)+(ch^),ch=getchar();
    }
    return x?sum:-sum;
}
inline void write(int x){
    if(x<)
        putchar('-'),x=-x;
    if(x>)
        write(x/);
    putchar(x%+'');
}
int mi(int x,int y){
    return x<y?x:y;
}
int ma(int x,int y){
    return x>y?x:y;
}
const int M=6e3+;
vector<int>g[M];
int f[M],dp[M][];

void dfs(int u){
    for(int i=;i<g[u].size();i++){
        int v=g[u][i];
        dfs(v);
        dp[u][]+=ma(dp[v][],dp[v][]);
        dp[u][]+=dp[v][];
    }
}
int main(){
    int n=read();

    for(int i=;i<=n;i++){
        dp[i][]=read();
    }
    while(true){
        int x=read(),y=read();
        if(!x&&!y)
            break;
        g[y].push_back(x);
        f[x]=y;
    }
    int root=;
    while(f[root]!=)
        root=f[root];
    dfs(root);
    write(ma(dp[root][],dp[root][]));
    return ;
}