ZOJ 3626 Treasure Hunt I / 树形DP

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也可以叫做树形背包因为在回溯的时候像01背包一样枚举每个物品从最大容量开始更新

这里的物品代表以i为根的子树

#include <cstdio>#include <cstring>#include <vector>#include <algorithm>using namespace std;const int maxn = 110;struct node{int e;int w;};int dp[maxn][maxn*2];vector <node> a[maxn];int b[maxn];bool vis[maxn];int n, s, m;void dfs(int u, int t){//if(vis[u][t])//return dp[u][t];if(t < 0)return;for(int i = 0; i <= t; i++)dp[u][i] = b[u];vis[u] = true;for(int i = 0; i < a[u].size(); i++){node v = a[u][i];if(vis[v.e])continue;dfs(v.e, t-2*v.w);for(int j = t; j >= 2*v.w; j--){for(int k = 0; k <= j-2*v.w; k++){node vv = a[v.e][i];dp[u][j] = max(dp[u][j], dp[u][j-k-2*v.w] + dp[v.e][k]);}}}}int main(){while(scanf("%d", &n) == 1){for(int i = 1; i <= n; i++){scanf("%d", &b[i]);a[i].clear();}for(int i = 1; i < n; i++){int u, v, w;scanf("%d %d %d", &u, &v, &w);a[u].push_back((node){v, w});a[v].push_back((node){u, w});}scanf("%d %d", &s, &m);memset(dp, 0, sizeof(dp));memset(vis, false, sizeof(vis));dfs(s, m);printf("%d\n", dp[s][m]);}return 0;}

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