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Added karatsuba algorithm for multiplying large numbers #239

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Added karatsuba algorithm for multiplying large numbers #239

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53 changes: 53 additions & 0 deletions Others/Karatsuba.java
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package Others;

/**
* Java Program to Implement Karatsuba Multiplication Algorithm.
* Mainly used for multiplication of large numbers.
* @author mani manasa mylavarapu
**/

import java.util.Scanner;

/** Class Karatsuba **/
public class Karatsuba {
/** Function to multiply two large numbers **/
public long multiply(long x, long y) {
int size1 = getNumberOfDigits(x);
int size2 = getNumberOfDigits(y);
int N = Math.max(size1, size2);
if (N < 10)
return x * y;
N = (N / 2) + (N % 2);
long m = (long) Math.pow(10, N);
long b = x / m;
long a = x - (b * m);
long d = y / m;
long c = y - (d * N);
long z0 = multiply(a, c);
long z1 = multiply(a + b, c + d);
long z2 = multiply(b, d);

return z0 + ((z1 - z0 - z2) * m) + (z2 * (long) (Math.pow(10, 2 * N)));
}

public int getNumberOfDigits(long num) {
int ctr = 0;
while (num != 0) {
ctr++;
num /= 10;
}
return ctr;
}

/** Main function for testing **/
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
Karatsuba karat = new Karatsuba();

System.out.println("Enter two numbers\n");
long num1 = scan.nextLong();
long num2 = scan.nextLong();
long product = karat.multiply(num1, num2);
System.out.println("\nProduct result is : " + product);
}
}