HDU4276 The Ghost Blows Light 树形DP

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做这个题的时候想到了，先来一遍最短路，判断是否可以到达，若可以减去最短路的花费，再在剩下的花费里进行DP求最优解，想到了但是没做到，很多细节没有处理好，结果崩盘了，唉，看题解很多人都是两边dfs，不过这位大牛也是先spfa了一遍，给我这个弱菜看看刚好，这篇好好记录下来，

最后参考了大牛的：http://blog.csdn.net/acm_cxlove/article/details/7964739，可以说是一模一样了

#include<iostream>#include<cstdio>#include<list>#include<algorithm>#include<cstring>#include<string>#include<queue>#include<stack>#include<map>#include<vector>#include<cmath>#include<memory.h>#include<set>#include<cctype>#define ll long long#define LL __int64#define eps 1e-8#define inf 0xfffffff//const LL INF = 1LL<<61;using namespace std;//vector<pair<int,int> > G;//typedef pair<int,int > P;//vector<pair<int,int> > ::iterator iter;////map<ll,int >mp;//map<ll,int >::iterator p;typedef struct Node {int fro,to;int nex;int val;};Node edge[100 * 4];int value[100 + 5];int head[100 + 5];bool vis[100 + 5];int dis[100 + 5];int father[100 + 5];int mark[100 + 5];int dp[100 + 5][500 + 5];int tot;int n,t;void init() {memset(head,-1,sizeof(head));memset(value,0,sizeof(value));memset(edge,0,sizeof(edge));memset(mark,0,sizeof(mark));memset(dp,0,sizeof(dp));tot = 0;}void add(int u,int v,int w) {edge[tot].fro = u;edge[tot].to = v;edge[tot].val = w;edge[tot].nex = head[u];head[u] = tot++;}void spfa() {for(int i=0;i<=n;i++)dis[i] = inf;dis[1] = 0;memset(vis,false,sizeof(vis));memset(father,0,sizeof(father));queue<int> q;int s = 1;q.push(s);vis[s] = true;while(!q.empty()) {int u = q.front();q.pop();vis[u] = false;for(int i = head[u];i != -1;i = edge[i].nex) {int v = edge[i].to;int val = edge[i].val;if(dis[v] > dis[u] + val) {dis[v] = dis[u] + val;father[v] = u;mark[v] = i;if(!vis[v]) {vis[v] = true;q.push(v);}}}}for(int i=n;i != 1;i=father[i])edge[mark[i]].val = 0;}void dfs(int u,int fa) {for(int i=head[u];i!=-1;i=edge[i].nex) {int v = edge[i].to;int val = edge[i].val * 2;if(v == fa)continue;dfs(v,u);for(int j=t;j>=val;j--)for(int k = j-val;k>=0;k--)dp[u][j] = max(dp[u][j],dp[u][k] + dp[v][j - k - val]);}for(int i=0;i<=t;i++)dp[u][i] += value[u];}int main() {while(scanf("%d %d",&n,&t) == 2) {init();for(int i = 1;i < n;i++) {int u,v,w;scanf("%d %d %d",&u,&v,&w);add(u,v,w);add(v,u,w);}for(int i = 1;i <= n;i++)scanf("%d",&value[i]);spfa();if(dis[n] > t) {puts("Human beings die in pursuit of wealth, and birds die in pursuit of food!");continue;}t -= dis[n];dfs(1,0);printf("%d\n",dp[1][t]);}return 0;}

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