树形DP

HDU 1520 Anniversary party

d[i][0]=以i为根的子树，不选择i时的最大值
d[i][1]=以i为根的子树，选择i时的最大值

d[i][0]=∑v为i的儿子max(d[v][0],d[v][1])
d[i][1]=∑v为i的儿子d[v][0]

#include<stdio.h>#include <iostream>#include<stdlib.h>#include<algorithm>#include<vector>#include<deque>#include<map>#include<set>#include<queue>#include<math.h>#include<string.h>#include<string>using namespace std;#define ll long long#define pii pair<int,int>const int inf = 1e9 + 7;const int N = 1e6 + 5;struct Edge{    int v,next;}edge[2*N];int head[N];inline void addEdge(int k,int u,int v){    edge[k].v=v;    edge[k].next=head[u];    head[u]=k;}int c[N];int d[N][2];int inDeg[N];int dp(int i,int j){    if(d[i][j]>0){        return d[i][j];    }    else{        d[i][j]=j?c[i]:0;        for(int k=head[i];k!=-1;k=edge[k].next){            int v=edge[k].v;            if(j==0){                d[i][j]+=max(dp(v,1),dp(v,0));            }            else{                d[i][j]+=dp(v,0);            }        }    }    return d[i][j];}int main(){    //freopen("/home/lu/Documents/r.txt","r",stdin);    //freopen("/home/lu/Documents/w.txt","w",stdout);    int n;    while(~scanf("%d",&n)){        for(int i=1;i<=n;++i){            d[i][0]=d[i][1]=-inf;            head[i]=-1;            scanf("%d",&c[i]);            inDeg[i]=0;        }        int l,k;        int nume=0;        while(scanf("%d%d",&l,&k),l+k){            addEdge(nume++,k,l);            ++inDeg[l];        }        int ans=0;        for(int i=1;i<=n;++i){            if(inDeg[i]==0){                ans+=max(dp(i,0),dp(i,1));            }        }        printf("%d\n",ans);    }    return 0;}