# Write algorithm for finding the gcd of a number

In this case 2 is not a common divisor. A formal proof would use mathematical induction. The algorithm runs very fast. That is, the computation used less than. The algorithm will become clearer when you see the flow chart of calculating GCD of two numbers using recursion as shown below.

The GCD must divide two of the three pieces in all of the equations, and thus must divide the third. Solution Write a function to find middle element of linked list in one pass? This algorithm may easily be programmed as follows: Since the GCD of and 45 is 15, we should be able to write 15 as a sum of multiples of and I will answer first question by giving a formal description of the algorithm, which supposedly finds the greatest common divisor GCD of two integers.

Therefore, the GCD also divides the "final b". This is true for every common divisor of a and b.

Binary method[ edit ] An alternative method of computing the gcd is the binary gcd method which uses only subtraction and division by 2. The latter algorithm is geometrical. This GCD definition led to the modern abstract algebraic concepts of a principal ideal an ideal generated by a single element and a principal ideal domain a domain in which every ideal is a principal ideal.

The GCD of two numbers is the largest positive integer that divides both the numbers fully i. Certain problems can be solved using this result. The process of substituting remainders by formulae involving their predecessors can be continued until the original numbers a and b are reached: Each of the above steps reduces at least one of a and b towards 0 and so can only be repeated a finite number of times.

Now let me take a fairly random integer, say Any number that divides a and b must also divide c so every common divisor of a and b is also a common divisor of b and c. This method will throw an error if the user will enter an invalid value instead of an integer.

Why does the algorithm stop? Therefore the "final b" must be a divisor of both of the initial a and initial b. There are five possibilities: In this case 2 is a common divisor. Divide both a and b by 2, increment d by 1 to record the number of times 2 is a common divisor and continue. Therefore r must eventually be 0.

Since 20 is less than 97, and 97 is prime, the GCD of 20 and 97 should be 1. In outline the method is as follows: The extended Euclidean algorithm described, for example, hereallows the computation of multiplicative inverses mod P. Therefore 34 is the multiplicative inverse of 20 mod As in the previous case 2 is not a common divisor.

Maintained by greenfie math. Several questions occur immediately. If you like this little programming exercise and hungry for more to improve your coding skill, check out these exercises, they will help to build your programming logic: Solution How to find Fibonacci sequence up to a given Number?

The Euclidean algorithm is one of the oldest algorithms in common use. Forcade [46] and the LLL algorithm. Replace a by b and replace b by r. You can also calculate greatest common divisor in Java without using recursion but that would not be as easy as the recursive version, but still a good exercise from coding interviews point of view.

Several novel integer relation algorithms have been developed, such as the algorithm of Helaman Ferguson and R.

BTW, there are a couple of other technique to find Greatest common divisor in Java, as an exercise you can explore those methods and write code for that.In mathematics, the greatest common divisor (gcd) of two or more integers, which are not all zero, is the largest positive integer that divides each of the integers.

For example, the gcd of 8 and 12 is 4. Division by two can be achieved by shifting the input number by one bit. Each step of the algorithm makes at least one such shift. The extended Euclidean algorithm (described, for example, here, allows the computation of multiplicative inverses mod P. First let's see an example.

First let's see an example. Since the GCD of and 45 is 15, we should be able to write 15 as a sum of multiples of and The greatest common divisor (GCD) of a and b is the largest number that divides both of them with no remainder.

One way to find the GCD of two numbers is Euclid’s algorithm, which is based on the. How to find GCD of two numbers in Java - Euclid's algorithm There are other methods as well to * find GCD of two number in Java but this example of finding GCD of two number * is most simple.

Write a Program to Check if a number is Power of Two or not? Sep 08,  · One way to write this, using the notation mod = the remainder is that GCD(a,b) = b if a mod b = 0, and GCD(a,b) = GCD(b, a mod b) otherwise. As an example, let's find GCD(,91).

First, use 77 instead ofso GCD(,91) becomes GCD(77,91)%(15). In mathematics, the Euclidean algorithm, or Euclid’s algorithm, is a method for computing the greatest common divisor (GCD) of two (usually positive) integers, also known as the greatest common factor (GCF) or highest common factor (HCF).

Write algorithm for finding the gcd of a number
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