HDOJ 4276 The Ghost Blows Light 树上分组背包
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先判断从1号点能否顺利到n号点,并记录路径,和所需的时间.
然后从1号点开始跑树上的分组背包,需要注意的是:
1. 原路径上的点的权值提前加出来.
2. 路径上的两个点间的边长重置为0.
dp方程:
设v点为u的孩子,c为u到v的边长,
u可能有很多个孩子,依次按上面转移跑很多遍01背包即可.
The Ghost Blows Light
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 2788 Accepted Submission(s): 862
Problem Description
My name is Hu Bayi, robing an ancient tomb in Tibet. The tomb consists of N rooms (numbered from 1 to N) which are connected by some roads (pass each road should cost some time). There is exactly one route between any two rooms, and each room contains some treasures. Now I am located at the 1st room and the exit is located at the Nth room.
Suddenly, alert occurred! The tomb will topple down in T minutes, and I should reach exit room in T minutes. Human beings die in pursuit of wealth, and birds die in pursuit of food! Although it is life-threatening time, I also want to get treasure out as much as possible. Now I wonder the maximum number of treasures I can take out in T minutes.
Input
There are multiple test cases.
The first line contains two integer N and T. (1 <= n <= 100, 0 <= T <= 500)
Each of the next N - 1 lines contains three integers a, b, and t indicating there is a road between a and b which costs t minutes. (1<=a<=n, 1<=b<=n, a!=b, 0 <= t <= 100)
The last line contains N integers, which Ai indicating the number of treasure in the ith room. (0 <= Ai <= 100)
Output
For each test case, output an integer indicating the maximum number of treasures I can take out in T minutes; if I cannot get out of the tomb, please output “Human beings die in pursuit of wealth, and birds die in pursuit of food!”.
Sample Input5 101 2 2 2 3 22 5 33 4 31 2 3 4 5Sample Output11
Source
2012 ACM/ICPC Asia Regional Changchun Online
/* ***********************************************Author :CKbossCreated Time :2015年09月09日 星期三 13时46分59秒File Name :HDOJ4276.cpp************************************************ */#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <string>#include <cmath>#include <cstdlib>#include <vector>#include <queue>#include <set>#include <map>using namespace std;const int maxn=200;const int inf=0x3f3f3f3f;int n,T;struct Edge{ int to,next,cost;}edge[maxn*2];int Adj[maxn],Size;void init(){ memset(Adj,-1,sizeof(Adj)); Size=0;}void Add_Edge(int u,int v,int c){ edge[Size].to=v; edge[Size].next=Adj[u]; edge[Size].cost=c; Adj[u]=Size++;}int dist[maxn],pre[maxn];int valu[maxn];void dfs(int u,int fa){ pre[u]=fa; for(int i=Adj[u];~i;i=edge[i].next) { int v=edge[i].to; int c=edge[i].cost; if(v==fa) continue; dist[v]=dist[u]+c; dfs(v,u); }}bool onroad[maxn];int ans;int findRoad(){ memset(onroad,false,sizeof(onroad)); int u=n,ret=0; while(u!=pre[u]) { ret+=valu[u]; valu[u]=0; onroad[u]=true; u=pre[u]; } onroad[1]=true; ret+=valu[1]; valu[1]=0; return ret;}int dp[maxn][5*maxn];//// fenzhu beibaovoid DP(int u,int fa){ for(int i=Adj[u];~i;i=edge[i].next) { int v=edge[i].to; int c=edge[i].cost; if(v==fa) continue; DP(v,u); if(onroad[u]&&onroad[v]) c=0; for(int vl=T;vl>=0;vl--) /// 容量 { for(int j=vl;j>=0;j--) /// 花费时间 { dp[u][vl]=max(dp[u][vl],dp[u][vl-j]+dp[v][j-c]); } } }}int main(){ //freopen("in.txt","r",stdin); //freopen("out.txt","w",stdout); while(scanf("%d%d",&n,&T)!=EOF) { init(); for(int i=0;i<n-1;i++) { int u,v,c; scanf("%d%d%d",&u,&v,&c); Add_Edge(u,v,c); Add_Edge(v,u,c); } for(int i=1;i<=n;i++) { scanf("%d",valu+i); pre[i]=i; ///init dp } memset(dist,63,sizeof(dist)); dist[1]=0; dfs(1,1); if(dist[n]>T) { puts("Human beings die in pursuit of wealth, and birds die in pursuit of food!"); continue; } //// find road ans=findRoad(); T-=dist[n]; T/=2; memset(dp,0,sizeof(dp)); for(int i=1;i<=n;i++) { for(int j=0;j<=T;j++) { if(onroad[i]==false) dp[i][j]=valu[i]; } } DP(1,1); printf("%d\n",dp[1][T]+ans); } return 0;}
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