CF533B Work Group

Jisoo

不显然的树上dp

定义\(f_{i,j}\)为第i位和为子树所选奇数个/偶数个点的方案数

然后显然会发现奇数加奇数等于偶数等规律

然后就可以转移了

#include<cstdio>
#include<iostream>
#include<cstring>
#include<iomanip>
#include<cmath>
#include<algorithm>
#define int long long
using namespace std;
template<class T>inline void read(T &x)
{
    x=0;register char c=getchar();register bool f=0;
    while(!isdigit(c))f^=c=='-',c=getchar();
    while(isdigit(c))x=(x<<3)+(x<<1)+(c^48),c=getchar();
    if(f)x=-x;
}
template<class T>inline void print(T x)
{
    if(x<0)putchar('-'),x=-x;
    if(x>9)print(x/10);
    putchar('0'+x%10);
}
int f[2000005][2];
int n;
struct e{
	int to;
	int ne;
}ed[200001];
int a[2000005];
int head[2000005];
int x,y;
int p;
void add(int f,int to){
	p++;
	ed[p].ne=head[f];
	ed[p].to=to;
	head[f]=p;
}
void dfs(int ro){
	f[ro][1]=-999999999;
	for(int i=head[ro];i;i=ed[i].ne){
		int v=ed[i].to;
		//if(v==fa) continue;
		dfs(v);
		int x=f[ro][0],y=f[ro][1];
		f[ro][0]=max(x+f[v][0],y+f[v][1]);
		f[ro][1]=max(x+f[v][1],y+f[v][0]);
	}
	f[ro][1]=max(f[ro][1],f[ro][0]+a[ro]);
}
signed main(){
	ios::sync_with_stdio(false);
	read(n);
	for(int i=1;i<=n;++i){
		read(x);
		read(a[i]);
		if(x!=-1) 
		add(x,i);
	}
	//memset(f,0xc0,sizeof(f));
	dfs(1);
	
	cout<<max(f[1][0],f[1][1]);
    return 0;
}