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;
}