BZOJ2435 [Noi2011]道路修建

这是NOI11年题，你在逗我？

直接dfs就可以了，Linux下貌似不会爆栈。。。

/**************************************************************
    Problem: 2435
    User: rausen
    Language: C++
    Result: Accepted
    Time:5184 ms
    Memory:76756 kb
****************************************************************/
 
#include <cstdio>
 
using namespace std;
typedef long long ll;
const int N = 1000005;
 
struct edge {
    int next, to, v;
    edge() {}
    edge(int _n, int _t, int _v) : next(_n), to(_t), v(_v) {}
} e[N << 1];
 
struct tree_node {
    int vis, sz;
} tr[N];
 
int first[N], tot;
int n;
ll ans;
 
inline int read() {
    int x = 0;
    char ch = getchar();
    while (ch < '0' || '9' < ch)
        ch = getchar();
    while ('0' <= ch && ch <= '9') {
        x = x * 10 + ch - '0';
        ch = getchar();
    }
    return x;
}
 
void Add_Edges(int x, int y, int z) {
    e[++tot] = edge(first[x], y, z), first[x] = tot;
    e[++tot] = edge(first[y], x, z), first[y] = tot;
}
 
inline int abs(int x) {
    return x < 0 ? -x : x;
}
 
#define y e[x].to
void dfs(int p) {
    int x;
    tr[p].vis = tr[p].sz = 1;
    for (x = first[p]; x; x = e[x].next)
        if (!tr[y].vis) {
            dfs(y);
            tr[p].sz += tr[y].sz;
            ans += 1ll * abs(n - (tr[y].sz << 1)) * e[x].v;
        }
}
#undef y
 
int main() {
    int i, x, y, z;
    n = read();
    for (i = 1; i < n; ++i) {
        x = read(), y = read(), z = read();
        Add_Edges(x, y, z);
    }
    dfs(1);
    printf("%lld
", ans);
    return 0;
}

(p.s. 貌似都找不到一个分类了。。。要死。。。就分在dfs序下好了)