簡(jiǎn)單的樹形dp

dp[i] 表示以i為根的包括i 的大歡樂度

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f[i] 表示以i為根不包括i 的大歡樂度

葉節(jié)點(diǎn)則為 f[i] = 0, dp[i] = w[i]  只要初始化 dp f 都全為0 就可以了 dfs會(huì)自動(dòng)復(fù)制

說實(shí)話我覺得這題很不嚴(yán)謹(jǐn) 他說歡樂度可以為負(fù)值  按理來說如果小于0 就應(yīng)該將歡樂度設(shè)為0 表示那個(gè)人不參加

最后是 無論設(shè)不設(shè)為0 都AC 證明根本沒有歡樂度為負(fù)值的

要注意的是

1. 不是只有一個(gè)case  我一開始以為只有一個(gè)case  一直錯(cuò) 要處理到?jīng)]有輸入為止。。。 題目又沒說明

2. 有可能有多棵樹 所以要多次dfs()

View Code

Anniversary party

Time Limit :2000/1000ms (Java/Other)   Memory Limit : 65536/32768K (Java/Other)
Total Submission(s) :5   Accepted Submission(s) : 2
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Problem Description
Thereis 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 numberedfrom 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
Output should contain the maximal sum of guests' ratings.Sample Input
711111111 32 36 47 44 53 50 0
Sample Output
5

View Code

#include <stdio.h>
#include<algorithm>
#include<string.h>

const int MAXN = 6005;
struct node
{
int index ;
    node*next ;
}adj[MAXN];
bool vis[MAXN], isRoot[MAXN];
int n, m, f[MAXN], dp[MAXN], w[MAXN]; 
void addEdge(int x, int y)
{
    node*p = new node;
    p->index = y;
    p->next = adj[x].next;
    adj[x].next= p;
    isRoot[y]= 0;
}
int max(int a, int b)
{return a>=b ?a :b  ;  }
void dfs(int root)
{
    vis[root]= 1;
    node*p = adj[root].next;
while( p != NULL )
    {
int u = p->index;
if(!vis[u])
        {
            dfs(u);
//    dp[root] += f[u]<0 ?0 :f[u];
//    int tmp = max(dp[u], f[u]);
//    f[root] += tmp < 0 ? 0 : tmp ;            dp[root] += f[u];
            f[root]+= max(dp[u], f[u]);
        }
        p= p->next;
    }
    dp[root]+= w[root];
}
int main()
{
int i, a, b, root, ans = 0;
while(scanf("%d", &n)!=EOF)
    {
        ans= 0;
for(i=1; i<=n; i++)
        {
            scanf("%d", &w[i]);
            isRoot[i]= 1; dp[i] = f[i] = 0;
            adj[i].next= NULL, vis[i] = 0;
        }
while(scanf("%d %d", &a, &b), a|b)
            addEdge(b, a);
for(i=1; i<=n; i++)
if(isRoot[i])
            {
                dfs(i);
                ans+= max(dp[i], f[i]);
            }
            printf("%d
", ans);
    }
return 0;
}

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