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=998244353;
const long maxn=1e5+5;
 
vector<int>e[maxn];
bool vis[maxn]={0};
ll result=0,x,y;
 
void gcd(ll a,ll b)
{
    if (b==0)
    {
        x=1;
        y=0;
    }
    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]=1;
    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+1);
}
 
int main()
{
    int n,i,x,y;
    scanf("%d",&n);
    for (i=1;i<n;i++)
    {
        scanf("%d%d",&x,&y);
        e[x].push_back(y);
        e[y].push_back(x);
    }
    dfs(1,1);
    printf("%lld",result);
    return 0;
}
/*
3
2 1
3 2
*/