python/TangDou/AcWing_TiGao/T5/QiWang/217.cpp

#include <bits/stdc++.h>
using namespace std;

const int N = 1e5 + 10, M = N << 1;

int n, m;
int h[N], e[M], ne[M], w[M], idx;
int out[N];
double f[N];

void add(int a, int b, int c) {
    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx++;
}
double dfs(int u) {
    if (f[u] >= 0) return f[u]; // 如果u点计算过，记忆化搜索返回结果值
    f[u] = 0;                   // 初始化为0，准备开始填充
    for (int i = h[u]; ~i; i = ne[i]) {
        int j = e[i];
        f[u] += (w[i] + dfs(j)) / out[u];
    }
    return f[u];
}
int main() {
    memset(h, -1, sizeof h);
    cin >> n >> m;
    while (m--) {
        int a, b, c;
        cin >> a >> b >> c;
        add(a, b, c);
        out[a]++;
    }
    memset(f, -1, sizeof f);
    printf("%.2lf\n", dfs(1));
    return 0;
}