I am trying to calculate the Greatest Common Divisor using a while loop. I am therefore looking for the greatest number (i.e. the last value of the loop). How do I get rid of the preceding numbers?
Example:
The greatest common divisor of 84 and 18 is 6. However, my code gives me the numbers 2, 3, and 6. What do I need to change to get only the last number?
using System;
namespace CalculateGCD
{
class Program
{
static void Main(string[] args)
{
int a = int.Parse(Console.ReadLine());
int b = int.Parse(Console.ReadLine());
int i = 1;
while (i <= Math.Min(a, b))
{
i++;
if (a % i == 0 && b % i == 0)
{
Console.WriteLine("GCD:{0}", i);
}
}
}
}
}
Define a variable called max then print the max out of the while loop like this:
int max = 0;
while (i <= Math.Min(a, b))
{
i++;
if (a % i == 0 && b % i == 0)
{
max = i;
}
}
Console.WriteLine("GCD:{0}", max);
Also if you are using C# 6 you could simplify your Console.WriteLine by using string interpolation like this:
Console.WriteLine($"GCD:{max}");
There is a simple solution which will calculate GCD
static int GCD(int a, int b) {
return b == 0 ? a : GCD(b, a % b);
}
and you can use it like below
using System;
namespace CalculateGCD
{
public class Program
{
public static void Main(string[] args)
{
int a = int.Parse(Console.ReadLine());
int b = int.Parse(Console.ReadLine());
Console.WriteLine(GCD(a,b));
}
static int GCD(int a, int b)
{
return b == 0 ? a : GCD(b, a % b);
}
}
}
You can invert the loop, insted of going from 1 to the Min between a and b, search from the Min to 1.
int i = Math.Min(a, b);
while (i > 0)
{
i--;
if (a % i == 0 && b % i == 0)
{
Console.WriteLine("GCD:{0}", i);
break;
}
}
simply reverse the enumeration sequence will do
int a = int.Parse(Console.ReadLine());
int b = int.Parse(Console.ReadLine());
int i = Math.Min(a ,b);
while (i > 1)
{
if (a % i == 0 && b % i == 0)
{
Console.WriteLine("GCD:{0}", i);
break;//greatest will be the first
}
i--;
}
int gcd;
while (i <= Math.Min(a, b))
{
i++;
if (a % i == 0 && b % i == 0)
{
gcd=i;
}
}
Console.WriteLine("GCD:{0}",gcd);
Save greatest common divisor in a variable.
Related
This is what I tried:
using System;
namespace OddAndEvenNumbers
{
class Program
{
static void Main(string[] args)
{
int requiredOddAndEvenNumbers = Convert.ToInt32(Console.ReadLine());
int oddNumbersCount = 0;
int evenNumbersCount = 0;
int n = Convert.ToInt32(Console.ReadLine());
while (oddNumbersCount <= requiredOddAndEvenNumbers || evenNumbersCount <= requiredOddAndEvenNumbers)
{
if (n % 2 == 0)
{
evenNumbersCount++;
}
else if (n % 2 != 0)
{
oddNumbersCount++;
}
}
Console.WriteLine(evenNumbersCount + " " + oddNumbersCount);
Console.ReadLine();
}
}
}
I don't know why it doesn't work.
The program should stop when odd numbers and even number equals N.
You never update n so the loop will never exit
So evenNumbersCount and oddNumbersCount will never count up
using System;
namespace OddAndEvenNumbers
{
class Program
{
static void Main(string[] args)
{
int requiredOddAndEvenNumbers = Convert.ToInt32(Console.ReadLine());
int oddNumbersCount = 0;
int evenNumbersCount = 0;
int n = Convert.ToInt32(Console.ReadLine());
while (oddNumbersCount <= requiredOddAndEvenNumbers || evenNumbersCount <= requiredOddAndEvenNumbers)
{
if (n % 2 == 0)
{
evenNumbersCount++;
}
else if (n % 2 != 0)
{
oddNumbersCount++;
}
n++;
}
Console.WriteLine(evenNumbersCount + " " + oddNumbersCount);
Console.ReadLine();
}
}
}
It seems you've forgotten to get new number inside the loop. It keeps checking the first number
ItThe while loop works until the Odd + Even numbers are equal to n.
int requiredOddAndEvenNumbers = Convert.ToInt32(Console.ReadLine());
int oddNumbersCount = 0;
int evenNumbersCount = 0;
int n = 0;
while ((oddNumbersCount + evenNumbersCount) < requiredOddAndEvenNumbers)
{
n = Convert.ToInt32(Console.ReadLine());
if (n % 2 == 0)
{
evenNumbersCount++;
}
else if (n % 2 != 0)
{
oddNumbersCount++;
}
}
Console.WriteLine("evenNumbersCount: {0}", evenNumbersCount);
Console.WriteLine("oddNumbersCount: {0}", oddNumbersCount);
I want to store integers(in an array or anything) that in range of int "i" and int "j".
eg:-Think, "int i = 1" and "int j = 10".I want to store integers from 1 and 10.
So that (1,2,3,4,5,6,7,8,9,10)
Because I want to answer to HackerRank "Beautiful Days at the Movies".
link below.
https://www.hackerrank.com/challenges/beautiful-days-at-the-movies/problem?isFullScreen=false
here is my code and it a garbage.
static int beautifulDays(int i, int j, int k) {
var total = 0;
for(var a = i; a <= j; a++ )
{
if (a != 0)
{
int ri = Reverse(i);
int rj = Reverse(j);
var ra = Reverse(a);
if((ra/k) % 1 == 0)
{
total++;
}
if((rj/k) % 1 == 0)
{
total++;
}
if((ri/k) % 1 == 0)
{
total++;
}
}
return total;
}
return total;
}
public static int Reverse(int inval)
{
int result = 0;
do
{
result = (result * 10) + (inval % 10);
inval = inval / 10;
}
while(inval > 0);
return result;
}
simply, can you give me the answer of HackerRank "Beautiful Days at the Movies".
link below.
https://www.hackerrank.com/challenges/beautiful-days-at-the-movies/problem?isFullScreen=false
Using Java you can easily stream a range of numbers with IntStream, then map the reverse function for each value, then filter those that fulfils the condition and count. With streams you don't need to store, you can get straight to the answer.
IntUnaryOperator reverse = (opperand) -> {
int reversed = 0;
int num = opperand;
while (num != 0) {
int digit = num % 10;
reversed = reversed * 10 + digit;
num /= 10;
}
return Math.abs(opperand - reversed);
};
return (int) IntStream.rangeClosed(i, j).map(reverse)
.filter(v -> v % k == 0).count();
The main part of my code is working, the only thing that doesn't work is the output of all its divisors. My result if it's not a prime should be like this:
Input -> 4
Output -> false 1 2 4
Console.WriteLine("Type your number: ");
int n = Convert.ToInt32(Console.ReadLine());
int a = 0, i;
for (i = 1; i <= n; i++)
{
if (n % i == 0)
{
a++;
}
}
if (a == 2)
{
Console.WriteLine("true");
}
else
{
Console.WriteLine("false" + i);
}
Console.ReadLine();
To print all the divisors, you'll need to gather them up in a collection of some sort – a list of integers, here.
In addition, all integers are divisible by 1, so you don't want to start there; neither do you want to end at n, since n % n == 0.
var divisors = new List<int>();
for (var i = 2; i < 2; i++)
{
if (n % i == 0)
{
divisors.Add(i);
}
}
if (divisors.Count == 0)
{
Console.WriteLine("true");
}
else
{
Console.WriteLine("false " + String.Join(" ", divisors));
}
Here is a working solution. You basically have to store your divisors somewhere or print them directly:
public static void Method(int n)
{
if (IsPrime(n))
{
Console.WriteLine($"{n} is a prime");
return;
}
var divisors = new List<int>();
for(var i = 1; i <= n; i++)
{
if (n % i == 0)
divisors.Add(i);
}
Console.WriteLine($"{n} isn't a prime");
Console.WriteLine($"The divisors are: {string.Join(", ", divisors)}");
}
public static bool IsPrime(int n)
{
for(var i = 2; i < n; i++)
{
if (n % i == 0)
return false;
}
return true;
}
From a brief inspection, there are two ways to generate the output. So far, you count the number of divisors, but neither store them nor write them to the output. You could replace
if (n % i == 0)
{
a++;
}
by
if (n % i == 0)
{
Console.WriteLine(i);
a++;
}
or store the divisors in a
List<int>
to generate the output afterwards.
Im currently trying to create a program that prints the prime numbers from 0 to 10,000 using only for,do while and ifs. I created this program but it doesn't runs
static void Main(string[] args)
{
for (int x = 2; x < 10000; x++)
{
for (int y = 1; y < x; y++)
{
if (x % y != 0)
{
Console.WriteLine(x);
}
}
Console.ReadKey();
}
I don't know where the problem is and also if the for inside resets.
Try this with no bool variable!!!:
static void Main(string[] args)
{
for (int x = 2; x < 10000; x++)
{
int isPrime = 0;
for (int y = 1; y < x; y++)
{
if (x % y == 0)
isPrime++;
if(isPrime == 2) break;
}
if(isPrime != 2)
Console.WriteLine(x);
isPrime = 0;
}
Console.ReadKey();
}
Check Console.ReadKey(); it should be after upper for loop, you can even change condition for upper for loot with <= since 10000 also need to check for prime condition.
Below is the efficient way to print prime numbers between 0 and 10000
using System.IO;
using System;
class Program
{
static void Main()
{
Console.WriteLine("Below are prime numbers between 0 and 10000!");
Console.WriteLine(2);
for(int i=3;i<=10000;i++)
{
bool isPrime=true;
for(int j=2;j<=Math.Sqrt(i);j++)
{
if(i%j==0)
{
isPrime=false;
break;
}
}
if(isPrime)
{
Console.WriteLine(i);
}
}
}
}
Is there any reason that you put Console.ReadKey(); inside of loop?
You should put that out of the loop unless press key during loop.
static void Main(string[] args)
{
for (int x = 2; x < 10000; x++)
{
for (int y = 1; y < x; y++)
{
if (x % y != 0)
{
Console.WriteLine(x);
}
}
}
Console.ReadKey();
}
And probably that code is just print lots of x.
You should to fix it.
The first problem is that x % 1 will always be zero, at least for non-zero x. You need to start the test (inner) loop at one and, for efficiency, stop when you've exceeded the square root of the number itself - if n has a factor f where f > sqrt(n), you would have already found the factor n / f.
The second problem is that you will write out a candidate number every time the remainder is non-zero. So, because 15 % 4 is three, it will be output despite the fact that fifteen is very much a non-prime. It will also be output at 15 % 2, 15 % 4, 15 % 6, 15 % 7, and so on.
The normal (naive) algorithm for prime testing is:
# All numbers to test.
foreach number 2..whatever:
# Assume prime, check all numbers up to squareroot(number).
isPrime = true
foreach test 2..infinity until test * test > number:
# If a multiple, flag as composite and stop inner loop.
if number % test == 0:
isPrime = false
exit foreach
end
end
# If never flagged as composite, output as prime.
if isPrime:
output number
end
Here is simple logic to Print Prime No for any upper limit.
Input : 10 Output : 2 , 3 , 5 ,7
namespace PurushLogics
{
class Purush_PrimeNos
{
static void Main()
{
//Prime No Program
bool isPrime = true;
Console.WriteLine("Enter till which number you would like print Prime Nos\n");
int n = int.Parse(Console.ReadLine());
Console.WriteLine("Prime Numbers : ");
for (int i = 2; i <= n; i++)
{
for (int j = 2; j <= n; j++)
{
if (i != j && i % j == 0)
{
isPrime = false;
break;
}
}
if (isPrime)
{
Console.Write("\t" + i);
}
isPrime = true;
}
Console.ReadKey();
}
}
}
Here is my code where you can generate and print the prime numbers between two numbers (in between string_starting_number and string_last_number). The lowest possible value for string_starting_number is 0 and the highest possible value for string_last_number is decimal.MaxValue-1=79228162514264337593543950334 and not 79228162514264337593543950335 because of the decimal_a++ command inside a for loop which will result to an overflow error.
Take note that you should input the values in string type in string_starting_number and in string_last_number.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace GeneratingPrimeNumbers
{
class Program
{
static void Main(string[] args)
{
string string_starting_number = "1"; //input here your choice of starting number
string string_last_number = "10"; //input here your choice of last number
decimal decimal_starting_number = Convert.ToDecimal(string_starting_number);
decimal decimal_last_number = Convert.ToDecimal(string_last_number);
string primenumbers = "";
ulong ulong_b;
ulong ulong_c;
if (decimal_starting_number <= ulong.MaxValue)
{
ulong ulong_starting_number = Convert.ToUInt64(decimal_starting_number);
ulong ulong_last_number;
if (decimal_last_number > ulong.MaxValue)
{
ulong_last_number = ulong.MaxValue;
}
else
{
ulong_last_number = Convert.ToUInt64(decimal_last_number);
}
if (ulong_starting_number == 0 || ulong_starting_number == 1 || ulong_starting_number == 2 || ulong_starting_number == 3)
{
primenumbers = 2 + " " + 3;
ulong_starting_number = 5;
}
if (ulong_starting_number % 2 == 0)
{
ulong_starting_number++;
}
ulong ulong_a;
for (ulong_a = ulong_starting_number; ulong_a <= ulong_last_number; ulong_a += 2)
{
ulong_b = Convert.ToUInt64(Math.Ceiling(Math.Sqrt(ulong_a)));
for (ulong_c = 3; ulong_c <= ulong_b; ulong_c += 2)
{
if (ulong_a % ulong_c == 0)
{
goto next_value_of_ulong_a;
}
}
primenumbers = primenumbers + " " + ulong_a;
next_value_of_ulong_a:
{
}
}
}
if (decimal_last_number > ulong.MaxValue)
{
string ulong_maximum_value_plus_two = "18446744073709551617";
if (decimal_starting_number <= ulong.MaxValue)
{
decimal_starting_number = Convert.ToDecimal(ulong_maximum_value_plus_two);
}
if (decimal_starting_number % 2 == 0)
{
decimal_starting_number++;
}
decimal decimal_a;
for (decimal_a = decimal_starting_number; decimal_a <= decimal_last_number; decimal_a += 2)
{
ulong_b = Convert.ToUInt64(Math.Ceiling(Math.Sqrt(ulong.MaxValue) * Math.Sqrt(Convert.ToDouble(decimal_a / ulong.MaxValue))));
for (ulong_c = 3; ulong_c <= ulong_b; ulong_c += 2)
{
if (decimal_a % ulong_c == 0)
{
goto next_value_of_decimal_a;
}
}
primenumbers = primenumbers + " " + decimal_a;
next_value_of_decimal_a:
{
}
}
}
Console.WriteLine(primenumbers);
Console.ReadKey();
}
}
}
I have a code here written in C# that finds the smallest multiple by all numbers from 1 to 20. However, I find it very inefficient since the execution took awhile before producing the correct answer. I would like to know what are the different ways that I can do to improve the code. Thank You.
public static void SmallestMultiple()
{
const ushort ARRAY_SIZE = 21;
ushort[] array = new ushort[ARRAY_SIZE];
ushort check = 0;
for (uint value = 1; value < uint.MaxValue; value++)
{
for (ushort j = 1; j < ARRAY_SIZE; j++)
{
array[j] = j;
if (value % array[j] == 0)
{
check++;
}
}
if (check == 20)
{
Console.WriteLine("The value is {0}", value);
}
else
{
check = 0;
}
}
}
static void Main(string[] args)
{
int[] nums = Enumerable.Range(1, 20).ToArray();
int lcm = 1;
for (int i = 0; i < nums.Length; i++)
{
lcm = LCM(lcm, nums[i]);
}
Console.WriteLine("LCM = {0}", lcm);
}
public static int LCM(int value1, int value2)
{
int a = Math.Abs(value1);
int b = Math.Abs(value2);
// perform division first to avoid potential overflow
a = checked((a / GCD(a, b)));
return checked((a * b));
}
public static int GCD(int value1, int value2)
{
int gcd = 1; // Greates Common Divisor
// throw exception if any value=0
if (value1 == 0 || value2 == 0)
{
throw new ArgumentOutOfRangeException();
}
// assign absolute values to local vars
int a = Math.Abs(value1); // local var1
int b = Math.Abs(value2); // local var2
// if numbers are equal return the first
if (a == b) { return a; }
// if var "b" is GCD return "b"
if (a > b && a % b == 0) { return b; }
// if var "a" is GCD return "a"
if (b > a && b % a == 0) { return a; }
// Euclid algorithm to find GCD (a,b):
// estimated maximum iterations:
// 5* (number of dec digits in smallest number)
while (b != 0)
{
gcd = b;
b = a % b;
a = gcd;
}
return gcd;
}
}
Source : Fast Integer Algorithms: Greatest Common Divisor and Least Common Multiple, .NET solution
Since the result must also be divisible by 19 (which is the greatest prime number) up to 20, you might only cycle through multiples of 19.
This should get to to the result about 19 times faster.
Here's the code that does this:
public static void SmallestMultiple()
{
const ushort ARRAY_SIZE = 21;
ushort[] array = new ushort[ARRAY_SIZE];
ushort check = 0;
for (uint value = 19; value < uint.MaxValue; value += 19)
{
for (ushort j = 1; j < ARRAY_SIZE; j++)
{
array[j] = j;
if (value % array[j] == 0)
{
check++;
}
}
if (check == 20)
{
Console.WriteLine("The value is {0}", value);
return;
}
else
{
check = 0;
}
}
}
On my machine, this finds the result 232792560 in a little over 2 seconds.
Update
Also, please note that the initial program did not stop when reaching a solution; I have added a return statement to make it stop.
You're just looking for the LCM of the numbers from 1 to 20:
Where the GCD can be efficiently calculated with the Euclidean algorithm.
I don't know C#, but this Python solution shouldn't be hard to translate:
def gcd(a, b):
while b != 0:
a, b = b, a % b
return a
def lcm(a, b):
return (a * b) / gcd(a, b)
numbers = range(1, 20 + 1)
print reduce(numbers, lcm)
It's pretty fast too:
>>> %timeit reduce(lcm, range(1, 20000))
1 loops, best of 3: 258 ms per loop
EDIT: v2.0 - Major speed improvement
Building on w0lf's solution. A faster solution:
public static void SmallestMultiple()
{
// this is a bit quick and dirty
// (not too difficult to change to generate primeProduct dynamically for any range)
int primeProduct = 2*3*5*7*11*13*17*19;
for (int value = primeProduct; ; value += primeProduct)
{
bool success = true;
for (int j = 11; j < 21; j++)
{
if (value % j != 0)
{
success = false;
break;
}
}
if (success)
{
Console.WriteLine("The value is {0}", value);
break;
}
}
}
You needn't check 1-10 since if something is divisible by x (e.g. 12), it is divisible by x/n (e.g. 12/2 = 6). The smallest multiple will always be a multiple of a product of all the primes involved.
Didn't benchmark C# solution, but equivalent Java solution runs in about 0.0000006 seconds.
Well I'm not sure what exactly you are trying to accomplish here but your out side for loop will run approximately 4,294,967,295 time (uint.MaxValue). So that will take some time...
If you have a way to keep from going to uint.MaxValue - like breaking your loop when you have accomplished what you need to - that will speed it up.
Also, since you are setting array[j] equal to j and then apparently never using the array again why not just do:
value % j
instead of
value % array[j]
Using also code written by W0lf (sorry but i cannot comment on your post) I would improve it (only a little) deleting the array that I think is useless..
public static void SmallestMultiple()
{
const ushort ARRAY_SIZE = 21;
ushort check = 0;
for (uint value = 1; value < uint.MaxValue; value++)
{
for (ushort j = 1; j < ARRAY_SIZE; j++)
{
if (value % j == 0)
{
check++;
}
}
if (check == 20)
{
Console.WriteLine("The value is {0}", value);
}
else
{
check = 0;
}
}
}