Submission #188129

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()
#define valid(y,x,h,w) (0<=y&&y<h&&0<=x&&x<w)
#define tpl(...) make_tuple(__VA_ARGS__)
const int INF = 0x3f3f3f3f;
const double EPS = 1e-8;
const double PI = acos(-1);
typedef long long ll;
typedef pair<int,int> pii;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
template<class T>ostream&operator<<(ostream &o,const vector<T>&t){o<<'[';FOR(i,t){if(i!=t.begin())o<<',';o<<*i;}return o<<']';}
template<class S,class T>ostream&operator<<(ostream &o,const pair<S,T>&t){return o<<'('<<t.first<<','<<t.second<<')';}
template<int N,class Tp>void out(ostream&,const Tp&){}
template<int N,class Tp,class,class ...Ts>void out(ostream &o,const Tp&t){if(N)o<<',';o<<get<N>(t);out<N+1,Tp,Ts...>(o,t);}
template<class ...Ts>ostream&operator<<(ostream&o,const tuple<Ts...>&t){o<<'(';out<0,tuple<Ts...>,Ts...>(o,t);return o<<')';}
template<class T>void output(T *a,int n){REP(i,n){if(i)cout<<',';cout<<a[i];}cout<<endl;}
template<class T>void output(T *a,int n,int m){REP(i,n)output(a[i],m);}
template<class T>void output(T t){if(t<0)t=-t,putchar(45);static int c[20];
int k=0;while(t)c[k++]=t%10,t/=10;for(k||(c[k++]=0);k;putchar(c[--k]^48));}
template<class S,class ...T>void output(S a,T...t){output(a);putchar(' ');output(t...);}
template<class T>bool input(T &t){int n=1,c;for(t=0;!isdigit(c=getchar())&&~c&&c-45;);
if(!~c)return 0;for(c-45&&(n=0,t=c^48);isdigit(c=getchar());t=10*t+c-48);t=n?-t:t;return 1;}
template<class S,class ...T>bool input(S&a,T&...t){input(a);return input(t...);}

#define double long double

double func(int n, int a) {
  double res = 1;
  REP(i,n) {
    res *= n-i;
    res /= 2;
    if (a-i>0) res /= a-i;
    if (n-a-i>0) res /= n-a-i;
  }
  return res;  
}
double solve(int n, int dx) {
  // a-b = dx
  // a+b = n
  // a = (dx+n)/2;
  if (dx>n) return 0.0;
  if ((dx+n)&1) return 0.0;
  int a = (dx+n)/2;
  return func(n,a);
}

int main() {
  ll n,d,x,y;
  while(cin>>n>>d>>x>>y) {
    if (x%d!=0 || y%d!=0 || abs(x)/d+abs(y)/d > n) {
      cout << 0 << endl;
      continue;
    }
    int dx = abs(x)/d;
    int dy = abs(y)/d;
    // cout << dx << " " << dy << endl;
    double ans = 0;
    REP(i,n+1) {
      int j = n-i;
      ans += solve(i,dx) * solve(j,dy) * func(n,i);
      // if (solve(i,dx) * solve(j,dy) == 0) {
      //   cout << i << " " << dx << " " << dy << endl;
      //   cout << solve(i,dx) << " " << solve(j,dy) << " " << func(n,i) << endl;
      // }
    }
    printf("%.12Lf\n", ans);
  }
}

Submission Info

Judge Result