bzoj1722: [Usaco2006 Mar] Milk Team Select 产奶比赛 树形dp

题目链接

bzoj1722: [Usaco2006 Mar] Milk Team Select 产奶比赛

题解

dp[i][j][0 / 1]
以i为根的子数中
相邻点对选了j个的最大价值

代码

#include<vector> 
#include<cstdio> 
#include<cstring> 
#include<algorithm> 
#define gc getchar() 
#define pc putchar 
inline int read() {
	int x = 0,f = 1; 
	char c = gc;  
	while(c < '0' || c > '9') {if(c == '-') f = - 1; c = gc;}  
	while(c <= '9' && c >= '0') x = x * 10 + c - '0',c = gc; 
	return x * f; 
} 
#define LL long long 
void print(int x) { 
	if(x >= 10) print(x / 10); 
	pc(x % 10 + '0'); 
} 
const int maxn = 501; 
const int maxm = 100007; 
struct node { 
	int v,next; 
} edge[maxn << 1]; 
int num = 0,head[maxn]; 
inline void add_edge(int u,int v) { 
	edge[++ num].v = v; edge[num].next = head[u];head[u] = num; 
} 
int val[maxn]; 
int n,x; 
int f[maxn][maxn][2]; 
int siz[maxn]; 
void dfs(int x) { 
	siz[x] = 1; 
	f[x][0][0] = f[x][0][1] = 0; 
	for(int i = head[x];i;i = edge[i].next) { 
		int v = edge[i].v; 
		dfs(v); 
		siz[x] += siz[v]; 
		for(int j = siz[x];j >= 0;-- j) 
			for(int k = 0;k <= std::min(j,siz[v]); ++ k) {
				f[x][j][0] = std::max(f[x][j][0], f[x][j - k][0] + std::max(f[v][k][0],f[v][k][1])); 
				if(k) f[x][j][1] = std::max(f[x][j][1], f[x][j - k][1] + f[v][k - 1][1]);  
				f[x][j][1] = std::max(f[x][j][1], f[x][j - k][1] + f[v][k][0]);  
			} 
	} 
	for(int i = siz[x];i >= 0;-- i) f[x][i][1] += val[x]; 
} 
int main() { 
	n = read(); x = read(); 
	memset(f,-0x3f,sizeof f); 
	for(int i = 1;i <= n;++ i) { 
		val[i] = read(); 
		add_edge(read(),i); 
	} 
	dfs(0); 
	for(int i = n;i >= 0;-- i) { 
		if(f[0][i][0] >= x) { 
			print(i); return 0; 
		} 
	} 
	pc('-'),pc('1'); 
	return 0; 
}