Day 4: Binomial Distribution I HackerRank Solution

Day 4: Binomial Distribution I HackerRank Solution
Source : https://www.hackerrank.com/challenges/s10-binomial-distribution-1

Objective
In this challenge, we learn about binomial distributions. Check out the Tutorial tab for learning materials!

Task
The ratio of boys to girls for babies born in Russia is . If there is child born per birth, what proportion of Russian families with exactly children will have at least boys?

Write a program to compute the answer using the above parameters. Then print your result, rounded to a scale of decimal places (i.e., format).

Input Format

A single line containing the following values:

1.09 1

If you do not wish to read this information from stdin, you can hard-code it into your program.

Output Format

Print a single line denoting the answer, rounded to a scale of decimal places (i.e., format).

Source : https://www.hackerrank.com/challenges/s10-binomial-distribution-1

Solution

	// github.com/RodneyShag
	public class Solution {
	public static void main(String[] args) {
	double ratio = 1.09; // hardcoded value
	double p = ratio / (1 + ratio);
	int n = 6;
	/* Calculate result */
	double result = 0;
	for (int x = 3; x <= n; x++) {
	result += binomial(n, x, p);
	}
	System.out.format("%.3f", result);
	}
	private static Double binomial(int n, int x, double p) {
	if (p < 0 || p > 1 || n < 0 || x < 0 || x > n) {
	return null;
	}
	return combinations(n, x) * Math.pow(p, x) * Math.pow(1 - p, n - x);
	}
	private static Long combinations(int n, int x) {
	if (n < 0 || x < 0 || x > n) {
	return null;
	}
	return factorial(n) / (factorial(x) * factorial(n - x));
	}
	private static Long factorial(int n) {
	if (n < 0) {
	return null;
	}
	long result = 1;
	while (n > 0) {
	result *= n--;
	}
	return result;
	}
	}