hdu 1520

树形dp

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <map>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <numeric>
#include <functional>
using namespace std;
#define LL long long
#define DB double
#define N 100005
const int INF = 0x3f3f3f3f;
const LL INFF = 1LL << 60;
const DB EPS = 1e-9;
const DB OO = 1e15;
const DB PI = acos(-1.0);
int val[N],dp[N][2],f[N];
vector<int>G[N];
void dfs(int rt)
{
    int i,len = G[rt].size();
    dp[rt][1] = val[rt];
    for(i = 0 ; i < len ; i++)
        dfs(G[rt][i]);
    for(i = 0 ; i < len ; i++)
    {
        dp[rt][0]+=max(dp[G[rt][i]][0],dp[G[rt][i]][1]);
        dp[rt][1]+=dp[G[rt][i]][0];
    }
}
int main()
{
    int n,i,j,a,b;

    while(~scanf("%d",&n))
    {
        memset(G,0,sizeof(G));
        for(i = 1 ; i <= n ; i++)
        {
            scanf("%d",&val[i]);
            f[i] = -1;
            dp[i][0] = dp[i][1] = 0;
        }
        while(scanf("%d %d",&a,&b),a+b)
        {
            f[a] = b;
            G[b].push_back(a);
        }
        a = 1;
        while(f[a]!=-1) a = f[a];
        dfs(a);
        printf("%d
",max(dp[a][0],dp[a][1]));
    }
    return 0;
}