牛客练习赛23 F 托米的游戏

https://www.nowcoder.com/acm/contest/156/F

树 概率

 #include <cstdio>
 #include <cstdlib>
 #include <cmath>
 #include <cstring>
 #include <string>
 #include <set>
 #include <map>
 #include <list>
 #include <stack>
 #include <queue>
 #include <vector>
 #include <algorithm>
 #include <iostream>
 using namespace std;
 #define ll long long
 #define minv 1e-6
 #define inf 1e9
 const ll mod=;
 const long maxn=1e5+;

 vector<int>e[maxn];
 bool vis[maxn]={};
 ll result=,x,y;

 void gcd(ll a,ll b)
 {
     if (b==)
     {
         x=;
         y=;
     }
     else
     {
         gcd(b,a%b);
         ll r;
         r=x;
         x=y;
         y=r-a/b*y;
     }
 }

 ll ni(ll s)
 {
     gcd(mod,s%mod);
     return (y%mod+mod)%mod;
 }

 void dfs(int d,int dep)
 {
     vis[d]=;
     result=(result+ni(dep))%mod;
     vector<int>::iterator i;
     for (i=e[d].begin();i!=e[d].end();i++)
         if (!vis[*i])
             dfs(*i,dep+);
 }

 int main()
 {
     int n,i,x,y;
     scanf("%d",&n);
     for (i=;i<n;i++)
     {
         scanf("%d%d",&x,&y);
         e[x].push_back(y);
         e[y].push_back(x);
     }
     dfs(,);
     printf("%lld",result);
     return ;
 }
 /*
 3
 2 1
 3 2
 */