題意：

某公司，每個人都有一個直接上司（除boss外且不存在環），每個人都有一個活躍值。現要舉行一個晚會，參加的人中不能有直接上司存在，問最大活躍值是多少？

解題思路：

任何一個人的來或不來可以看作一種決策，那么狀態就是在某個人來的時候或者不來的時候，以他為根的子樹能有的最大活躍總值。分別可以用dp[i][1]和dp[i][0]表示第i個人來和不來。

所以可以得到狀態轉移方程：

第i個人來：dp[i][1] += dp[child][0](他的直接下屬一定不能來)

第i個人不來：dp[i][0] += max ( dp[child][0], dp[child][1])(他的直接下屬可來可不來，取較大值)

代碼：

#include<iostream>#include<cstdio>#include<vector>#include<cstring>using namespace std;const int maxn = 1e4+5;vector<int> m[maxn];int n, dp[maxn][2], book[maxn];void dfs(int r){    for(int i = 0; i < m[r].size(); i++)    {        int child = m[r][i];        dfs(child);        dp[r][1] += dp[child][0];        dp[r][0] += max(dp[child][0], dp[child][1]);    }}int main(void){    while(cin >> n)    {        memset(dp, 0, sizeof(dp));        for(int i = 0; i < maxn; i++)            m[i].clear();        for(int i = 1; i <= n; i++)            scanf("%d", &dp[i][1]);        int x, y;        for(int i = 2; i <= n; i++)        {            scanf("%d%d", &x, &y);            book[x] = 1;            m[y].push_back(x);        }        scanf("%d%d", &x, &y);        int root;        for(int i = 1; i <= n; i++)            if(!book[i])            {                root = i;                break;            }        dfs(root);        PRintf("%d/n", max(dp[root][0], dp[root][1]));    }    return 0;}
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.InputEmployees 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 OutputOutput should contain the maximal sum of guests' ratings.Sample Input
711111111 32 36 47 44 53 50 0Sample Output
5