CodeForces

CodeForces - 1087D
https://vjudge.net/problem/2115151/origin
2*和/叶子结点的个数

#include<iostream>
#include<cstdio>
#include<queue>
#include<algorithm>
#include<cmath>
#include<ctime>
#include<set>
#include<map>
#include<stack>
#include<cstring>
#define inf 2147483647
#define ls rt<<1
#define rs rt<<1|1
#define lson ls,nl,mid,l,r
#define rson rs,mid+1,nr,l,r
#define N 1000010
#define For(i,a,b) for(int i=a;i<=b;i++)
#define p(a) putchar(a)
#define g() getchar()

using namespace std;
int n,x,y,cnt;
double t;
int a[N];
void in(int &x){
    int y=1;
    char c=g();x=0;
    while(c<'0'||c>'9'){
        if(c=='-')y=-1;
        c=g();
    }
    while(c<='9'&&c>='0'){
        x=(x<<1)+(x<<3)+c-'0';c=g();
    }
    x*=y;
}
void o(int x){
    if(x<0){
        p('-');
        x=-x;
    }
    if(x>9)o(x/10);
    p(x%10+'0');
}
int main(){
    in(n);
    cin>>t;
    For(i,1,n-1){
        in(x);in(y);
        a[x]++;
        a[y]++;
    }
    For(i,1,n)
        if(a[i]==1)
            cnt++;
    t=t*2.0/(double)cnt;
    printf("%.18f",t);
    return 0;
}