poj 2342(樹形DP)

Anniversary party

Time Limit: 1000MS

Memory Limit: 65536K

Total Submissions: 6062

Accepted: 3490

Description

There is going to be a party to celebrate the 80-th Anniversary of the Ural State University. The University has a hierarchical structure of employees. It means that the supervisor relation forms a tree rooted at the rector V. E. Tretyakov. In order to make the party funny for every one, the rector does not want both an employee and his or her immediate supervisor to be present. The personnel office has evaluated conviviality of each employee, so everyone has some number (rating) attached to him or her. Your task is to make a list of guests with the maximal possible sum of guests' conviviality ratings.

Input

Employees are numbered from 1 to N. A first line of input contains a number N. 1 <= N <= 6 000. Each of the subsequent N lines contains the conviviality rating of the corresponding employee. Conviviality rating is an integer number in a range from -128 to 127. After that go N – 1 lines that describe a supervisor relation tree. Each line of the tree specification has the form:

L K

It means that the K-th employee is an immediate supervisor of the L-th employee. Input is ended with the line

0 0

Output

Output should contain the maximal sum of guests' ratings.

Sample Input

Sample Output

Source

Ural State University Internal Contest October'2000 Students Session

狀壓太難,先做樹形DP

題意：某大學開一個晚會,有N個人,每個人都有自己的愉悅值，如果某人的上司在場那個人就會非常掃興,是以上司和下屬隻能去一個，問怎樣安排愉悅值最大。

分析：dp[i][0] 代表第i個人不去能夠獲得的最大愉悅值,以i為根的子樹能夠獲得的最大愉悅值

        dp[i][1] 代表第i個人去了能夠獲得的最大愉悅值,以i為根的子樹能夠獲得的最大愉悅值

dp[i][1] = dp[i][1] + dp[j][0] j為i的孩子

dp[i][0] = dp[i][0] + max(dp[j][0],dp[j][1])

由于這是單向邊，找到根節點後進行DFS，然後選出 max(dp[root][0],dp[root][1])