POJ 1463 Strategic game 最小点覆盖集（树形dp）

Description

Bob enjoys playing computer games, especially strategic games, but sometimes he cannot find the solution fast enough and then he is very sad. Now he has the following problem. He must defend a medieval city, the roads of which form a tree. He has to put the minimum number of soldiers on the nodes so that they can observe all the edges. Can you help him? 

Your program should find the minimum number of soldiers that Bob has to put for a given tree. 

For example for the tree: 

the solution is one soldier ( at the node 1).

Input

Output

Sample Input

4
0:(1) 1
1:(2) 2 3
2:(0)
3:(0)
5
3:(3) 1 4 2
1:(1) 0
2:(0)
0:(0)
4:(0)

Sample Output

1
2

Source

//6508K	375MS
#include<stdio.h>
#include<string.h>
#include<algorithm>
#define M 1507
using namespace std;
int head[M],nodes;
int dp[M][M];
struct E
{
    int v,next;
}edge[M*M];
void addedge(int u,int v)
{
    edge[nodes].v=v;edge[nodes].next=head[u];
    head[u]=nodes++;
}
void DP(int u,int p)
{
    dp[u][0]=1;
    dp[u][1]=0;
    int k,v;
    for(k=head[u];k!=-1;k=edge[k].next)
    {
        v=edge[k].v;
        if(v==p)continue;
        DP(v,u);
        dp[u][0]+=min(dp[v][0],dp[v][1]);
        dp[u][1]+=dp[v][0];
    }
}
int main()
{
    int n;
    while(scanf("%d",&n)!=EOF)
    {
        memset(head,-1,sizeof(head));
        nodes=0;
        int u,k,v;
        for(int i=0;i<n;i++)
        {
            scanf("%d:(%d)",&u,&k);
            while(k--)
            {
                scanf("%d",&v);
                addedge(u,v);
                addedge(v,u);
            }
        }
        DP(0,0);
        printf("%d\n",min(dp[0][0],dp[0][1]));
    }
    return 0;
}