Submission #188220

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Source Code Expand

import java.math.BigDecimal;
import java.math.BigInteger;
import java.math.RoundingMode;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {		
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int D = sc.nextInt();
		int x = sc.nextInt();
		int y = sc.nextInt();
		if (Math.abs(x)%D !=0 || Math.abs(y)%D != 0) {
			System.out.println(0);
			return;
		}
		x = Math.abs(x)/D;
		y = Math.abs(y)/D;
		if (x+y>n || (n+x+y)%2==1) {
			System.out.println(0);
			return;
		}
		
		BigInteger[] fact = new BigInteger[1001];
		fact[0] = BigInteger.ONE;
		for(int i=1;i<=1000;i++) {
			fact[i] = fact[i-1].multiply(BigInteger.valueOf(i));
		}		
		BigInteger sum = BigInteger.ZERO;
		BigDecimal pow = BigDecimal.valueOf(Math.pow(4, n));
		
		for(int a=x;(n+x+y)/2-a>=y;a++) {
			int b = a-x;
			int c = (n+x+y)/2-a;
			int d = c-y;
			sum = sum.add(fact[n].divide(fact[a]).divide(fact[b]).divide(fact[c]).divide(fact[d]));
		}
		
		double ans = new BigDecimal(sum).setScale(10).divide(pow,RoundingMode.HALF_UP).doubleValue();
		System.out.println(ans);
	}

}

Submission Info

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