Daily Problem #14

This problem was asked by Google.

The area of a circle is defined as πr^2. Estimate π to 3 decimal places using a Monte Carlo method.

Hint: The basic equation of a circle is x2 + y2 = r2.

int num = 100000000;
double distance = 0;
int hitPot = 0;
for (int i = 0;i < num;i++) {
    double x = 2 * Math.random();
    double y = 2 * Math.random();
    //System.out.println("(" + x + "," + y +")");
    distance = Math.sqrt(Math.pow((x - 1),2) + Math.pow((y - 1),2));
    if (distance < 1) {
        hitPot ++;
    }
}
BigDecimal b = new BigDecimal(hitPot).divide(new BigDecimal(num),8,BigDecimal.ROUND_DOWN).multiply(new BigDecimal(4));
double PI = b.doubleValue();
System.out.println( "hitPot = " +hitPot + "  PI = " + PI);