2435: [Noi2011]道路修建

Posted 2020-12-02 HWIM

2435: [Noi2011]道路修建

 

https://www.lydsy.com/JudgeOnline/problem.php?id=2435

 

 

 1 /*
 2 
 3 开始读错题了，以为顺序修建给定的边，计算费用，算的样例是12。
 4 每条边的权值就是两边的点的差的绝对值*这条边的长度。
 5 dfs一遍 
 6 
 7 */
 8 
 9 #include<bits/stdc++.h>
10 using namespace std;
11 typedef long long LL;
12  
13 inline int read() {
14     int x=0,f=1;char ch=getchar();for(;!isdigit(ch);ch=getchar())if(ch==‘-‘)f=-1;
15     for (;isdigit(ch);ch=getchar())x=x*10+ch-‘0‘;return x*f;
16 }
17 
18 const int N = 1000005;
19 int head[N],nxt[N<<1],to[N<<1],val[N<<1],siz[N],Enum,Sum;
20 LL Ans; // --- 
21 
22 inline void add_edge(int u,int v,int w) {
23     ++Enum;to[Enum] = v, val[Enum] = w, nxt[Enum] = head[u],head[u] = Enum;
24 }
25 void dfs(int u,int fa) {
26     siz[u] = 1;
27     for (int i=head[u]; i; i=nxt[i]) {
28         int v = to[i];
29         if (v == fa) continue;
30         dfs(v,u);
31         siz[u] += siz[v];
32         Ans += 1ll * abs(Sum - siz[v] - siz[v]) * val[i];
33     }
34 }
35 int main() {
36     int n = read();Sum = n;
37     for (int i=1; i<n; ++i) {
38         int u = read(),v = read(),w = read();
39         add_edge(u,v,w);add_edge(v,u,w);
40     }
41     dfs(1,0);
42     cout << Ans;
43     return 0;
44 }