The Weight of Tree

時間限制：3000?ms ?|? 內存限制：65535?KB 難度：4 描述

456 has a tree of n nodes, each node is assigned with an integer number. Now 456 wants to select a subtree, such that the sum of all integers on the nodes of the subtree is maxmized. Can you help him?? 輸入

On the first line of the input is an integer T, and then T cases follows. Each case begins with a positive integer n(1 <= n <= 10^5), then n numbers Wi(-1000 <= Wi <= 1000),Wi for the number on the ith node. Then n - 1 lines follows, each line contains two numbers a, b(1 <= a, b <= n)indicate that there is a edge between node a and b.

輸出

For each test case, output one integer on a line, the maximized sum can be achieved by selecting a subtree.?

樣例輸入

3 1 5 2 5 -5 1 2 5 -2 -3 7 -1 4 1 2 2 3 3 4 2 5

樣例輸出

5 5 8 ? ? 從第一個點一直往下深搜，然后回溯，判斷子節點的值是否大于0，如果大于0，父節點的值變為當前的值加上子節點的值。最后輸出最大值即可。

#include<stdio.h> #include<string.h> #include<vector> #include<algorithm> #define N 100005 using namespace std; vector<int> vec[N]; int vis[N],dp[N],MAX; void dfs(int x) {vis[x]=1;for(int i=0;i<vec[x].size();i++){int y=vec[x][i];if(vis[y])continue;dfs(y);if(dp[y]>0)dp[x]+=dp[y];MAX=max(dp[x],MAX);} } int main() {int t,n,i,a,b;scanf("%d",&t);while(t--){memset(vis,0,sizeof(vis));memset(vec,0,sizeof(vec));scanf("%d",&n);MAX=-999999;for(i=1;i<=n;i++){scanf("%d",&dp[i]);MAX=max(dp[i],MAX);}for(i=1;i<n;i++){scanf("%d%d",&a,&b);vec[a].push_back(b);vec[b].push_back(a);}dfs(1);printf("%d\n",MAX);}return 0; }

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