Submission #4657885

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Source Code Expand

#include <bits/stdc++.h>
#define For(i, a, b) for(int (i)=(a); (i)<(b); (i)++)
#define rFor(i, a, b) for(int (i)=(a)-1; (i)>=(b); (i)--)
#define rep(i, n) For((i), 0, (n))
#define rrep(i, n) rFor((i), (n), 0)
using namespace std;
typedef long long int lint;

vector<double> fact;

void setfact(int n){
    fact.resize(n+1);
    fact[0] = 1;
    rep(i, n) fact[i+1] = fact[i] * (i+1) / 4;
}

double getC(int n, int r){
    return fact[n] / fact[r] / fact[n-r];
}

int main(){
    int n, d, x, y; cin >> n >> d >> x >> y;
    setfact(n);
    double ans = 0;
    rep(i, n+1)rep(j, n+1){
        int k = (i*d - x) / d;
        int l = (j*d - y) / d;
        if(0<=k && k<=n && 0<=l && l<=n && (i-k)*d == x && (j-l)*d == y && i+j+k+l == n){
            ans += getC(n, i) / pow(4, i) * getC(n-i, j) / pow(4, j) * getC(n-i-j, k) / pow(4, k) * getC(n-i-j-k, l) / pow(4, l);
        }
    }
    cout << fixed << setprecision(10) << ans << endl;
}

Submission Info

Judge Result