SCU 4519 來個簽到吧 (exgcd推廣+概率dp)
阿新 • • 發佈:2019-02-10
題目傳送門:http://acm.scu.edu.cn/soj/problem.action?id=4519
這題開頭給你一些球,然後把任意球的編號之差
前面加球,任意兩個球
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <cmath>
#include <string>
#include <vector>
#include <cstdio>
#include <cctype>
#include <cstring>
#include <sstream>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#pragma comment(linker,"/STACK:102400000,102400000")
using namespace std;
#define MAX 100005
#define MAXN 1000005
#define maxnode 10
#define sigma_size 2
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define lrt rt<<1
#define rrt rt<<1|1
#define middle int m=(r+l)>>1
#define LL long long
#define ull unsigned long long
#define mem(x,v) memset(x,v,sizeof(x))
#define lowbit(x) (x&-x)
#define pii pair<int,int>
#define bits(a) __builtin_popcount(a)
#define mk make_pair
#define limit 10000
//const int prime = 999983;
const int INF = 0x3f3f3f3f;
const LL INFF = 0x3f3f;
const double pi = acos(-1.0);
const double inf = 1e18;
const double eps = 1e-9;
const LL mod = 1e9+7;
const ull mxx = 1333331;
/*****************************************************/
inline void RI(int &x) {
char c;
while((c=getchar())<'0' || c>'9');
x=c-'0';
while((c=getchar())>='0' && c<='9') x=(x<<3)+(x<<1)+c-'0';
}
/*****************************************************/
int gcd(int a,int b){
if(!b) return a;
return gcd(b,a%b);
}
double dp[MAX];
int main(){
//freopen("in.txt","r",stdin);
int t;
cin>>t;
while(t--){
int n;
cin>>n;
int tmp,maxn=0;
int flag=0;
for(int i=0;i<n;i++){
int b;
scanf("%d",&b);
if(i==0) tmp=b;
else tmp=gcd(tmp,b);
maxn=max(maxn,b);
if(b==0) flag=1;
}
int num=maxn/tmp+flag;
int add=num-n;
dp[num]=0;
//cout<<num<<endl;
for(int i=num-1;i>=0;i--){
dp[i]=dp[i+1]+num*1.0/(num-i);
}
int ans=dp[0]+add;
cout<<ans<<endl;
}
return 0;
}