Submission #1694752

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;

#define fi first
#define se second
#define repl(i,a,b) for(ll i=(ll)(a);i<(ll)(b);i++)
#define rep(i,n) repl(i,0,n)
#define each(itr,v) for(auto itr:v)
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl
#define mmax(x,y) (x>y?x:y)
#define mmin(x,y) (x<y?x:y)
#define maxch(x,y) x=mmax(x,y)
#define minch(x,y) x=mmin(x,y)
#define uni(x) x.erase(unique(all(x)),x.end())
#define exist(x,y) (find(all(x),y)!=x.end())
#define bcnt __builtin_popcount

#define INF INT_MAX/3

//// Matrix
//// calc with matrix
typedef vector<double> vec;
typedef vector<vec> mat;
struct Matrix{
  int N;
  mat a;
  Matrix(int n){
    N=n;
    a=mat(N,vec(N));
    for(int i=0;i<N;i++)a[i][i]=1;
  }
  Matrix pow(long long b) const {
    Matrix res(N);
    Matrix d(N);
    for(int i=0;i<N;i++)for(int j=0;j<N;j++)d[i][j]=a[i][j];
    for(;b>0;b>>=1,d=d*d)if(b&1)res=d*res;
    return res;
  }
  Matrix operator+(const Matrix& r) const {
    Matrix s(N);
    for(int i=0;i<N;i++){
      for(int j=0;j<N;j++){
        s[i][j]=(a[i][j]+r.a[i][j]);
      }
    }
    return s;
  }
  Matrix operator*(const Matrix& r) const {
    Matrix s(N);
    for(int i=0;i<N;i++)s[i][i]=0;
    for(int i=0;i<N;i++){
      for(int k=0;k<N;k++){
        for(int j=0;j<N;j++){
          s[i][j]+=a[i][k]*r.a[k][j];
        }
      }
    }
    return s;
  }

  vector<double>& operator[](int i){
    return a[i];
  }
};

int main(){
  double p;
  ll n;
  cin>>p>>n;
	Matrix m(2);
  m[0][0]=1-p; m[0][1]=p;
  m[1][0]=p; m[1][1]=1-p;
  Matrix res=m.pow(n);
  printf("%.15f\n", res[0][1]);
	return 0;
}

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