HDU 5834 Magic boy Bi Luo with his excited tree 树形DP

Magic boy Bi Luo with his excited tree

题目连接：

http://acm.hdu.edu.cn/showproblem.php?pid=5834

Description

Bi Luo is a magic boy, he also has a migic tree, the tree has N nodes , in each node , there is a treasure, it's value is V[i], and for each edge, there is a cost C[i], which means every time you pass the edge i , you need to pay C[i].

You may attention that every V[i] can be taken only once, but for some C[i] , you may cost severial times.

Now, Bi Luo define ans[i] as the most value can Bi Luo gets if Bi Luo starts at node i.

Bi Luo is also an excited boy, now he wants to know every ans[i], can you help him?

Input

First line is a positive integer T(T≤104) , represents there are T test cases.

Four each test：

The first line contain an integer N(N≤105).

The next line contains N integers V[i], which means the treasure’s value of node i(1≤V[i]≤104).

Output

For the i-th test case , first output Case #i: in a single line , then output N lines , for the i-th line , output ans[i] in a single line.

Sample Input

1
5
4 1 7 7 7
1 2 6
1 3 1
2 4 8
3 5 2

Sample Output

Case #1:
15
10
14
9
15

Hint

题意

给你一棵树，边有边权，每经过边一次，就得支付过路费c[i]，点上面有宝藏，每个点只能拿一次。

问从每个点出发，能够拿到的最大值是多少？

题解：

显然的树形DP

dfs两次，第一次dfs维护从这个点的子树出去，再回来能够取得的最大值是多少，不回来的最大值是多少。

然后第二次dfs，再加上从fa那儿转移过来的值就好了，同样维护回来，和不回来。

显然答案就是max(从fa回来+从子树不回来,从fa不回来+从子树回来）

树形DP维护一下这些玩意儿就好了。

代码

// writted by dnvtmf
#include <bits/stdc++.h>
#define INF 1000000007
#define FI first
#define SE second
#define PB emplace_back
#define VI vector<int>
using namespace std;
typedef long long LL;
typedef pair <int, int> P;
const int NUM = 100010;
struct edge {int next, to, cost;} e[NUM * 2];
int head[NUM], tot;
void gInit() {memset(head, -1, sizeof(head)); tot = 0;}
void add_edge(int u, int v, int c)
{
    e[tot] = (edge) {head[u], v, c};
	head[u] = tot++;
}
int n, V[NUM], w1[NUM], w2[NUM], id[NUM], ans[NUM];
//w1是从该点出发最后回到该点的最大值
//w2是从该点出发有一次不回来的最大值
//id是不回来的路的子树根节点
void dfs1(int u, int fa)
{
	w1[u] = V[u];
	w2[u] = V[u];
	id[u] = -1;
	for(int i = head[u]; ~i; i = e[i].next) {
		int v = e[i].to;
		if(v == fa) continue;
		dfs1(v, u);
		int tmp = max(0, w1[v] - e[i].cost - e[i].cost);
		int tmmp = w1[u] + max(0, w2[v] - e[i].cost);
		w2[u] += tmp;
		if(w2[u] < tmmp) {
			w2[u] = tmmp;
			id[u] = v;
		}
		w1[u] += tmp;
	}
}
//sum1同w1,sum2同w2
void dfs2(int u, int fa, int sum1, int sum2)
{
	ans[u] = max(w1[u] + sum2, w2[u] + sum1);
	int W1 = w1[u];
	int W2 = w2[u];
	int Id = id[u];
	W2 += sum1;
	if(W2 <= W1 + sum2) {
		W2 = W1 + sum2;
		Id = fa;
	}
	W1 += sum1;
	for(int i = head[u]; ~i; i = e[i].next) {
		int v = e[i].to;
		if(v == fa) continue;
		if(v == Id) {
			int tmp1 = sum1 + V[u], tmp2 = sum2 + V[u];
			for(int j = head[u]; ~j; j = e[j].next) {
				int vv = e[j].to;
				if(vv == fa || v == vv) continue;
				int tmp = max(0, w1[vv] - e[j].cost - e[j].cost);
				tmp2 = max(tmp1 + max(0, w2[vv] - e[j].cost), tmp2 + tmp);
				tmp1 += tmp;
			}
			tmp1 = max(0, tmp1 - e[i].cost - e[i].cost);
			tmp2 = max(0, tmp2 - e[i].cost);
			dfs2(v, u, tmp1, tmp2);
		}
		else {
			int tmp = max(0, w1[v] - e[i].cost - e[i].cost);
			int tmp1 = max(0, W1 - tmp - e[i].cost - e[i].cost);
			int tmp2 = max(0, W2 - tmp - e[i].cost);
			dfs2(v, u, tmp1, tmp2);
		}
	}
}
int main()
{
	int T; scanf("%d", &T);
	for(int cas = 1; cas <= T; ++cas) {
		gInit();
		scanf("%d", &n);
		for(int i = 1; i <= n; ++i) {
			scanf("%d", &V[i]);
		}
		for(int i = 1; i < n; ++i) {
			int u, v, c;
			scanf("%d%d%d", &u, &v, &c);
			add_edge(u, v, c);
			add_edge(v, u, c);
		}
		dfs1(1, -1);
		dfs2(1, -1, 0, 0);
		printf("Case #%d:
", cas);
		for(int i = 1; i <= n; ++i)
			printf("%d
", ans[i]);
	}
	return 0;
}