[BZOJ 3036] 绿豆蛙的归宿

[题目链接]

          https://www.lydsy.com/JudgeOnline/problem.php?id=3036

[算法]

        拓扑排序 + 概率DP

[代码]

         

#include<bits/stdc++.h>
using namespace std;
#define MAXN 100010

struct edge
{
    int to,w,nxt;
} e[MAXN << 1];

int tot;
queue< int > q;
int head[MAXN],in[MAXN],out[MAXN];
double f[MAXN];

template <typename T> inline void read(T &x)
{
    int f = 1; x = 0;
    char c = getchar();
    for (; !isdigit(c); c = getchar()) if (c == '-') f = -f;
    for (; isdigit(c); c = getchar()) x = (x << 3) + (x << 1) + c - '0';
    x *= f;
}
inline void addedge(int u,int v,int w)
{
    tot++;
    e[tot] = (edge){v,w,head[u]};
    head[u] = tot;
}

int main()
{
    
    int n,m;
    read(n); read(m);
    for (int i = 1; i <= m; i++)
    {
        int a,b,c;
        read(a); read(b); read(c);
        addedge(b,a,c);
        out[a]++;
        in[a]++;
    }
    q.push(n);
    while (!q.empty())
    {
        int cur = q.front();
        q.pop();
        for (int i = head[cur]; i; i = e[i].nxt)
        {
            int v = e[i].to , w = e[i].w;
            f[v] += (f[cur] + w) / (in[v] * 1.0);
            if (!(--out[v])) q.push(v);    
        }
    }
    printf("%.2lf\n",f[1]);
    
    return 0;
}