HDU 1011 (tree DP + backpack)

Question Link: Http://acm.hdu.edu.cn/showproblem.php? PID = 1, 1011

Theme: Retrieve the vertex from the tree. First retrieve the father and then the son. For each vertex, the weight is W, the cost is cost, and the maximum weight is obtained for the given total m consumption.

Solutions:

Tree Type backpack template question. First, create an undirected graph.

Cost = (Bug [root] + 19)/20 for each point, that is, if the number of bugs is less than 20, you need to send a person.

Use DP [I] [J] to represent the maximum cost of J in the I-root subtree.

Transition equation: DP [I] [J] = max (DP [I] [J], DP [I] [J-K] + dp [T] [k]), t is one of the sons, and K is the cost assigned to the sons.

Use DFS to perform DP for each root.

For each DFS ~ M is initialized. The value is W [root], indicating that only the father is used.

Then perform DFS for each son, each of which is a two for loop.

For (M... j... cost)

For (1... k... j-cost) // The son can allocate up to J-cost

The final result is DP [1] [m], where 1 is the total root point.

Note that m can be equal to 0 in this question. Therefore, After all data is read, 0 is output for the 0 feature; otherwise, DFS is used.

 

#include "cstdio"#include "vector"#include "cstring"using namespace std;#define maxn 500int bug[maxn],w[maxn],head[maxn],n,m,u,v,tol;struct Edge{    int to,next;}e[maxn*2];bool vis[maxn];int dp[maxn][maxn];void addedge(int u,int v){    e[tol].to=v;    e[tol].next=head[u];    head[u]=tol++;}void dfs(int root,int pre){    int i=root,cost=(bug[root]+19)/20;    for(int i=cost;i<=m;i++) dp[root][i]=w[root];    for(int a=head[root];a!=-1;a=e[a].next)    {        int t=e[a].to;        if(t==pre) continue;        dfs(t,root);        for(int j=m;j>=cost;j--)            for(int k=1;k<=j-cost;k++)                dp[i][j]=max(dp[i][j],dp[i][j-k]+dp[t][k]);    }}int main(){    //freopen("in.txt","r",stdin);    while(~scanf("%d%d",&n,&m)&&n>0)    {        memset(head,-1,sizeof(head));        memset(dp,0,sizeof(dp));        tol=0;        for(int i=1;i<=n;i++)            scanf("%d%d",&bug[i],&w[i]);        for(int i=1;i<n;i++)        {            scanf("%d%d",&u,&v);            addedge(u,v);            addedge(v,u);        }        if(m==0) {printf("0\n");continue;}        dfs(1,1);        printf("%d\n",dp[1][m]);    }    return 0;}

 

11488265

12:44:12

Accepted

1011

62 Ms

1280 K

1508 B

C ++

Physcal

HDU 1011 (tree DP + backpack)