树状结构 | 北邮OJ | 105. 寻找宝藏

版权声明：本文纯属作者口胡，欢迎转载 https://blog.csdn.net/TQCAI666/article/details/86757060

https://vpn.bupt.edu.cn/http/10.105.242.80/problem/p/105/

#include <bits/stdc++.h>
#define FF(a,b) for(int a=0;a<b;a++)
#define F(a,b) for(int a=1;a<=b;a++)
#define LEN 100
#define INF 1000000
#define bug(x) cout<<#x<<"="<<x<<endl;

using namespace std;
typedef long long ll;
const double pi=acos(-1);

typedef struct Node{
    int i,p;
    vector<int> c;
}Node;

Node tree[1010];

int main()
{
//    freopen("./in","r",stdin);
    int N,M,T,a,b;
    scanf("%d%d%d",&N,&M,&T);
    FF(i,N) tree[i].i=i;
    while(M--){
        scanf("%d%d",&a,&b);
        tree[a].c.push_back(b);
        tree[b].p=a;
    }
    int mul=1;
    while(1){
        int p=tree[T].p;
        mul*=tree[p].c.size();
        if(!p) break;
        else T=p;
    }
    printf("%.6f\n",1./mul);
    return 0;
}