题目
题目链接:http://acm.hdu.edu.cn/showproblem.php?pid=6822
题意:把一个纸对折(可以横对折、纵对折)n次,求它的最后有多少片的期望
思路
见这个大佬的博客->推导过程
代码
#include<cstdio>
#include<cstring>
#include<cmath>
#include<cstdlib>
#include<cctype>
#include<ctime>
#include<iostream>
#include<string>
#include<map>
#include<queue>
#include<stack>
#include<set>
#include<vector>
#include<iomanip>
#include<list>
#include<bitset>
#include<sstream>
#include<fstream>
#include<complex>
#include<algorithm>
#if __cplusplus >= 201103L
#include <unordered_map>
#include <unordered_set>
#endif
#define int long long
using namespace std;
const int mod=998244353;
int inv2 = 499122177;
const int INF = 0x3f3f3f3f;
int quick_pow(int a,int b){
int res=1;
while(b){
if(b&1){
res=res*a%mod;
}
b>>=1;
a=a*a%mod;
}
return res;
}
signed main(){
ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
int t;
cin>>t;
while(t--){
int n;
cin>>n;
int m=quick_pow(2,n);
cout<<((m+1)%mod+(2*quick_pow(3%mod,n)%mod*quick_pow(m,mod-2)%mod)%mod)%mod<<endl;
}
return 0;
}