Appoint description:
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)
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 Input
5 10
1 2 2
2 3 2
2 5 3
3 4 3
1 2 3 4 5
Sample Output
11
解题报告:
因为是一棵树,所以起点到终点的路径已经确定了,所以我们可以先暴力出所有路径上的点。
这样路径就是一条链了,之后我们在这条链上每个点进行一次树形背包,然后点之间的转移依旧用背包,就可以得出最终答案了,可以预先处理处1->n的距离,判断无解情况.
#include <iostream> #include <cstdio> #include <cstring> #include <algorithm> #include <vector> #include <map> using namespace std; const int maxn = 1e2 + 15; struct Edge {int v,nxt,w;}; Edge e[maxn*5]; int n , T , head[maxn] , tot , val[maxn] , dp[maxn][maxn*5] , ban[maxn] , ans[2][maxn*5] , mat[maxn][maxn]; vector< int >path; void addedge(int u ,int v,int w) {e[tot].v=v,e[tot].nxt=head[u],e[tot].w=w,head[u]=tot++;} bool dfs_path(int u,int fa) { if(u==n) { path.push_back(u); return true; } for(int i = head[u] ; ~i ; i = e[i].nxt) { int v = e[i].v; if(v==fa) continue; if(dfs_path(v,u)) { path.push_back(u); return true; } } return false; } inline void updata(int & x ,int v) { x = max( x , v); } void dfs(int u ,int fa) { for(int i = 0 ; i <= T ; ++ i) dp[u][i] = val[u]; for(int i = head[u] ; ~i ; i = e[i].nxt) { int v = e[i].v; if(v == fa || ban[v]) continue; dfs( v , u ); for(int j = T ; j >= 0 ; -- j) { int w = e[i].w; for(int k = T - j - w * 2 ; k >= 0 ; -- k) updata( dp[u][j + k + w * 2] , dp[u][j] + dp[v][k]); } } } int main(int argc,char *argv[]) { while(~scanf("%d%d",&n,&T)) { memset(head,-1,sizeof(head));tot=0;path.clear();memset(ban , 0 , sizeof(ban));memset( ans , 0 , sizeof(ans) ); int costall=0; int cur = 0; for(int i = 1 ; i < n ; ++ i) { int u , v , w;scanf("%d%d%d",&u,&v,&w); addedge( u , v , w); addedge( v , u , w); mat[u][v] = mat[v][u] = w; } for(int i = 1 ; i <= n ; ++ i) scanf("%d",val+i); dfs_path(1,0) ; reverse(path.begin() , path.end()); for(int i = 0 ; i < path.size() - 1 ; ++ i) costall += mat[path[i]][path[i+1]]; if(costall > T) { printf("Human beings die in pursuit of wealth, and birds die in pursuit of food!\n"); continue; } costall = 0; for(int i = 0 ; i < path.size() - 1 ; ++ i) { int cost = mat[path[i]][path[i+1]]; ban[path[i]]=1; ban[path[i+1]] = 1; int pre = cur ; cur ^= 1;memset(ans[cur] , 0 , sizeof(ans[cur])); int u = path[i]; dfs( u , -1); for(int j = T ; j >= costall ; -- j) for(int k = T - j - cost; k >=0 ; -- k) updata( ans[cur][j + k + cost] , ans[pre][j] + dp[u][k]); costall += cost; } int res = 0; dfs( n , -1); for(int i = T ; i >= costall ; -- i) for(int j = T - i ; j >= 0 ; -- j) res = max( res , ans[cur][i] + dp[n][j]); printf("%d\n",res); } return 0; }
No Pain , No Gain.