HDU 1520 Anniversary party (DFS or tree DP)

HDU 1520 Anniversary party (DFS or tree DP)
Problem 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 T 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 shoshould contain the maximal sum of guests ratings.

Sample Input

711111111 32 36 47 44 53 50 0

Sample Output

5

N people go to the party. A party with a direct relationship between superiors and subordinates will affect the atmosphere. Therefore, they cannot attend the party. Everyone will have an activity, now you need to calculate the number of people selected from n to maximize the activity of the party.
Idea: It is very simple. Each participant and not attending will have different results. If he participates, he only needs to add the weight of his subordinates who do not participate. He does not participate, then, with the maximum number of employees who participate or do not participate in the event, you only need to calculate the maximum number of students who participate or do not participate in the event.
PS: for the tree-like DP code, refer to other people's code. Recently, the blue bridge cup is being trained, so the DFS capability is enhanced.
AC code:

#include
 
  #define N 6005struct p{    int fm;    int child;    int brother;    int att;    int no;    void init()    {        no=0;        fm=0;        brother=0;        child=0;    }    int Max()    {        return att>no? att:no;    }}num[N];void dfs(int x){    int child=num[x].child;    while(child)    {        dfs(child);        num[x].att+=num[child].no;        num[x].no+=num[child].Max();        child=num[child].brother;    }}int main(){    int n;    while(~scanf("%d",&n))    {        for(int i=1;i<=n;i++)        {            num[i].init();            scanf("%d",&num[i].att);        }        int a,b;        while(scanf("%d %d",&a,&b),a||b)        {            num[a].fm=b;            num[a].brother=num[b].child;            num[b].child=a;        }        for(int i=1;i<=n;i++)        {            if(num[i].fm==0)            {                dfs(i);                printf("%d\n",num[i].Max());                break;            }        }    }    return 0;}