public static BigInteger find(BigInteger A,BigInteger B)
{
BigInteger res=BigInteger.ONE;
for(BigInteger i=A;i.compareTo(B)!=0;i.add(BigInteger.ONE))
res=res.add(i);
/*for(BigInteger i=1;i.compareTo(B)!=0;i.add(BigInteger.ONE))
res=res.multiply(A);*/
return res;
}
my intention is to add any 2 numbers within the range., let's say 2 to 5(2+3+4+5) or A raise to B. I have other option to get it done within BigInteger, but can anybody say what's wrong with the above snippet in which
Its producing longggggggggggggggggggggggggggggggg strange number(instead of original) and
Its struggling/juggling so much to increment by 1 as it normally increment outside/without loop?
When will it reach just one increment(time or space factor/performance)?
The sum of all integers in a range can be calculated as the average value multiplied by the number of values, aka the "count".
If A and B are both inclusive, as indicated by the "2 to 5(2+3+4+5)" text in the question, then we have:
average = (A + B) / 2
count = B - A + 1
sum = count * average
= (B - A + 1) * ((A + B) / 2)
= (B - A + 1) * (B + A) / 2 // flipped A + B for the symmetry of it
In Java code, using BigInteger, that means:
public static BigInteger sumRangeInclusive(BigInteger A, BigInteger B) {
return B.subtract(A).add(BigInteger.ONE).multiply(B.add(A)).shiftRight(1);
}
It seems there is an issue with storing value of the loop variable after increment.
The sum of arithmetic progression should include both A and B:
public static BigInteger find(BigInteger A,BigInteger B)
{
BigInteger sum = BigInteger.ZERO;
for (BigInteger i = A; i.compareTo(B) <=0; i = i.add(BigInteger.ONE)) {
sum = sum.add(i);
}
return sum;
}
Tests:
System.out.println(find(new BigInteger("2"), BigInteger.valueOf(5)));
System.out.println(find(new BigInteger("200"), BigInteger.valueOf(500)));
Output:
14
105350
my option for A raises to B without generating multiple instances
public static BigInteger find(BigInteger A,BigInteger B)
{
BigInteger res=BigInteger.ONE;
int b=B.intValue();
for(int i=1;i<=b;i++)
res=res.multiply(A);
return res;
}
A better way to solve this would be by applying simple arithmetic. We know that:
Sum of natural numbers up to n = n * (n + 1) / 2
Sum of natural numbers from m to n = Sum of natural numbers up to n minus Sum of natural numbers up to m - 1 = n * (n + 1) / 2 - (m - 1) * (m - 1 + 1) / 2 = n * (n + 1) / 2 - (m - 1) * (m) / 2 = (n * (n + 1) - (m - 1) * m) / 2.
Demo:
import java.math.BigInteger;
public class Main {
public static void main(String[] args) {
System.out.println(find(BigInteger.valueOf(123456789), BigInteger.valueOf(987654321)));
}
public static BigInteger find(BigInteger A, BigInteger B) {
return B.multiply(B.add(BigInteger.ONE)).subtract(A.subtract(BigInteger.ONE).multiply(A))
.divide(BigInteger.TWO);
}
}
Output:
480109740075445815
What is wrong with your code?
The loop terminates when A becomes equal to B whereas it should terminate when A becomes greater than B. For this, you can use the terminating condition as i.compareTo(B.add(BigInteger.ONE)) != 0.
A BigInteger is an immutable arbitrary-precision integer. Therefore, i.add(BigInteger.ONE) won't modify the value of i. You need to assign the result to i i.e. i = i.add(BigInteger.ONE) in order to increment the value referenced by i by one.
You have started with a value 1 (i.e. BigInteger res=BigInteger.ONE) instead of 0.
Correct code:
import java.math.BigInteger;
public class Main {
public static void main(String[] args) {
System.out.println(find(BigInteger.valueOf(2), BigInteger.valueOf(5)));
}
public static BigInteger find(BigInteger A, BigInteger B) {
BigInteger res = BigInteger.ZERO;
for (BigInteger i = A; i.compareTo(B.add(BigInteger.ONE)) != 0; i = i.add(BigInteger.ONE))
res = res.add(i);
return res;
}
}
Output:
14
Although you can get the correct result after correcting your code this way, it's performance will be extremely bad.
I'm trying to write a method that will calculate if two numbers are relatively prime for an assignment. I'm primarily looking for answers on where to start. I know there is a method gcd() that will do a lot of it for me, but the assignment is pretty much making me do it without gcd or arrays.
I kind of have it started, because I know that I will have to use the % operator in a for loop.
public static boolean relativeNumber(int input4, int input5){
for(int i = 1; i <= input4; i++)
Obviously this method is only going to return true or false because the main function is only going to print a specific line depending on if the two numbers are relatively prime or not.
I'm thinking I will probably have to write two for loops, both for input4, and input5, and possibly some kind of if statement with a logical && operand, but I'm not sure.
Well in case they are relatively prime, the greatest common divider is one, because - if otherwise - both numbers could be devided by that number. So we only need an algorithm to calculate the greatest common divider, for instance Euclid's method:
private static int gcd(int a, int b) {
int t;
while(b != 0){
t = a;
a = b;
b = t%b;
}
return a;
}
And then:
private static boolean relativelyPrime(int a, int b) {
return gcd(a,b) == 1;
}
Euclid's algorithm works in O(log n) which thus is way faster than enumerating over all potential divisors which can be optimized to O(sqrt n).
Swift 4 code for #williem-van-onsem answer;
func gcd(a: Int, b: Int) -> Int {
var b = b
var a = a
var t: Int!
while(b != 0){
t = a;
a = b;
b = t%b;
}
return a
}
func relativelyPrime(a : Int, b: Int) -> Bool{
return gcd(a: a, b: b) == 1
}
Usage;
print(relativelyPrime(a: 2, b: 4)) // false
package stack;
import java.util.Scanner; //To read data from console
/**
*
* #author base
*/
public class Stack {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
Scanner in = new Scanner(System.in); // with Scanner we can read data
int a = in.nextInt(); //first variable
int b = in.nextInt(); //second variable
int max; // to store maximum value from a or b
//Let's find maximum value
if (a >= b) {
max = a;
} else {
max = b;
}
int count = 0; // We count divisible number
for (int i=2; i<=max; i++) { // we start from 2, because we can't divide on 0, and every number divisible on 1
if (a % i == 0 && b % i==0) {
count++; //count them
}
}
if (count == 0) { // if there is no divisible numbers
System.out.println("Prime"); // that's our solutions
} else {
System.out.println("Not Prime"); //otherwise
}
}
}
I think that, this is the simple solution. Ask questions in comments.
I have a question regarding the CountDiv problem in Codility.
The problem given is: Write a function:
class Solution { public int solution(int A, int B, int K); }
that, given three integers A, B and K, returns the number of integers within the range [A..B] that are divisible by K, i.e.:
{ i : A ≤ i ≤ B, i mod K = 0 }
My code:
class Solution {
public int solution(int A, int B, int K) {
int start=0;
if (B<A || K==0 || K>B )
return 0;
else if (K<A)
start = K * ( A/K +1);
else if (K<=B)
start = K;
return (B-start+1)/K+ 1;
}
}
I don't get why I'm wrong, specially with this test case:
extreme_ifempty
A = 10, B = 10, K in {5,7,20}
WRONG ANSWER
got 1 expected 0
if K =5 then with i=10 A<=i<=B and i%k =0 so why should I have 0? Problem statement.
This is the O(1) solution, which passed the test
int solution(int A, int B, int K) {
int b = B/K;
int a = (A > 0 ? (A - 1)/K: 0);
if(A == 0){
b++;
}
return b - a;
}
Explanation: Number of integer in the range [1 .. X] that divisible by K is X/K. So, within the range [A .. B], the result is B/K - (A - 1)/K
In case A is 0, as 0 is divisible by any positive number, we need to count it in.
Java solution with O(1) and 100% in codility, adding some test cases with solutions for those who want to try and not see others solutions:
// Test cases
// [1,1,1] = 1
// [0,99,2] = 50
// [0, 100, 3] = 34
// [11,345,17] = 20
// [10,10,5] = 1
// [3, 6, 2] = 2
// [6,11,2] = 3
// [16,29,7] = 2
// [1,2,1] = 2
public int solution(int A, int B, int K) {
int offsetForLeftRange = 0;
if ( A % K == 0) { ++offsetForLeftRange; }
return (B/K) - (A /K) + offsetForLeftRange;
}
The way to solve this problem is by Prefix Sums as this is part of that section in Codility.
https://codility.com/programmers/lessons/3/
https://codility.com/media/train/3-PrefixSums.pdf
Using this technique one can subtract the count of integers between 0 and A that are divisible by K (A/K+1) from the the count of integers between 0 and B that are divisible by K (B/K+1).
Remember that A is inclusive so if it is divisible then include that as part of the result.
Below is my solution:
class Solution {
public int solution(int A, int B, int K) {
int b = (B/K) + 1; // From 0 to B the integers divisible by K
int a = (A/K) + 1; // From 0 to A the integers divisible by K
if (A%K == 0) { // "A" is inclusive; if divisible by K then
--a; // remove 1 from "a"
}
return b-a; // return integers in range
}
}
return A==B ? (A%K==0 ? 1:0) : 1+((B-A)/K)*K /K;
Well it is a completely illegible oneliner but i posted it just because i can ;-)
complete java code here:
package countDiv;
public class Solution {
/**
* First observe that
* <li> the amount of numbers n in [A..B] that are divisible by K is the same as the amount of numbers n between [0..B-A]
* they are not the same numbes of course, but the question is a range question.
* Now because we have as a starting point the zero, it saves a lot of code.
* <li> For that matter, also A=-1000 and B=-100 would work
*
* <li> Next, consider the corner cases.
* The case where A==B is a special one:
* there is just one number inside and it either is divisible by K or not, so return a 1 or a 0.
* <li> if K==1 then the result is all the numbers between and including the borders.
* <p/>
* So the algorithm simplifies to
* <pre>
* int D = B-A; //11-5=6
* if(D==0) return B%K==0 ? 1:0;
* int last = (D/K)*K; //6
* int parts = last/K; //3
* return 1+parts;//+1 because the left part (the 0) is always divisible by any K>=1.
* </pre>
*
* #param A : A>=1
* #param B : 1<=A<=B<=2000000000
* #param K : K>=1
*/
private static int countDiv(int A, int B, int K) {
return A==B ? A%K==0 ? 1:0 : 1+((B-A)/K)*K /K;
}
public static void main(String[] args) {
{
int a=10; int b=10; int k=5; int result=1;
System.out.println( a + "..." + b + "/" + k + " = " + countDiv(a,b,k) + (result!=countDiv(a,b,k) ? " WRONG" :" (OK)" ));
}
{
int a=10; int b=10; int k=7; int result=0;
System.out.println( a + "..." + b + "/" + k + " = " + countDiv(a,b,k) + (result!=countDiv(a,b,k) ? " WRONG" :" (OK)" ));
}
{
int a=6; int b=11; int k=2; int result=3;
System.out.println( a + "..." + b + "/" + k + " = " + countDiv(a,b,k) + (result!=countDiv(a,b,k) ? " WRONG" :" (OK)" ));
}
{
int a=6; int b=2000000000; int k=1; int result=b-a+1;
System.out.println( a + "..." + b + "/" + k + " = " + countDiv(a,b,k) + (result!=countDiv(a,b,k) ? " WRONG" :" (OK)" ));
}
}
}//~countDiv
I think the answers above don't provide enough logical explanation to why each solution works (the math behind the solution) so I am posting my solution here.
The idea is to use the arithmetic sequence here. If we have first divisible number (>= A) and last divisible number (<= B) we have an arithmetic sequence with distance K. Now all we have to do is find the total number of terms in the range [newA, newB] which are total divisible numbers in range [newA, newB]
first term (a1) = newA
last/n-th term (an) = newB
distance (d) = K
Sn = a1 + (a1+K) + (a1 + 2k) + (a1 + 3k) + ... + (a1 + (n-1)K)
`n` in the above equation is what we are interested in finding. We know that
n-th term = an = a1 + (n-1)K
as an = newB, a1 = newA so
newB = newA + (n-1)K
newB = newA + nK - K
nK = newB - newA + K
n = (newB - newA + K) / K
Now that we have above formula so just apply it in code.
fun countDiv(A: Int, B: Int, K: Int): Int {
//NOTE: each divisible number has to be in range [A, B] and we can not exceed this range
//find the first divisible (by k) number after A (greater than A but less than B to stay in range)
var newA = A
while (newA % K != 0 && newA < B)
newA++
//find the first divisible (by k) number before B (less than B but greater than A to stay in range)
var newB = B
while (newB % K != 0 && newB > newA)
newB--
//now that we have final new range ([newA, newB]), verify that both newA and newB are not equal
//because in that case there can be only number (newA or newB as both are equal) and we can just check
//if that number is divisible or not
if (newA == newB) {
return (newA % K == 0).toInt()
}
//Now that both newA and newB are divisible by K (a complete arithmetic sequence)
//we can calculate total divisions by using arithmetic sequence with following params
//a1 = newA, an = newB, d = K
// we know that n-th term (an) can also be calculated using following formula
//an = a1 + (n - 1)d
//n (total terms in sequence with distance d=K) is what we are interested in finding, put all values
//newB = newA + (n - 1)K
//re-arrange -> n = (newB - newA + K) / K
//Note: convert calculation to Long to avoid integer overflow otherwise result will be incorrect
val result = ((newB - newA + K.toLong()) / K.toDouble()).toInt()
return result
}
I hope this helps someone. FYI, codility solution with 100% score
Simple solution in Python:
def solution(A, B, K):
count = 0
if A % K == 0:
count += 1
count += int((B / K) - int(A / K))
return count
explanation:
B/K is the total numbers divisible by K [1..B]
A/K is the total numbers divisible by K [1..A]
The subtracts gives the total numbers divisible by K [A..B]
if A%K == 0, then we need to add it as well.
This is my 100/100 solution:
https://codility.com/demo/results/trainingRQDSFJ-CMR/
class Solution {
public int solution(int A, int B, int K) {
return (B==0) ? 1 : B/K + ( (A==0) ? 1 : (-1)*(A-1)/K);
}
}
Key aspects of this solution:
If A=1, then the number of divisors are found in B/K.
If A=0, then the number of divisors are found in B/K plus 1.
If B=0, then there is just one i%K=0, i.e. zero itself.
Here is my simple solution, with 100%
https://app.codility.com/demo/results/trainingQ5XMG7-8UY/
public int solution(int A, int B, int K) {
while (A % K != 0) {
++A;
}
while (B % K != 0) {
--B;
}
return (B - A) / K + 1;
}
Python 3 one line solution with score 100%
from math import ceil, floor
def solution(A, B, K):
return floor(B / K) - ceil(A / K) + 1
This works with O(1) Test link
using System;
class Solution
{
public int solution(int A, int B, int K)
{
int value = (B/K)-(A/K);
if(A%K == 0)
{
value=value+1;
}
return value;
}
}
I'm not sure what are you trying to do in your code, but simpler way would be to use modulo operator (%).
public int solution(int A, int B, int K)
{
int noOfDivisors = 0;
if(B < A || K == 0 || K > B )
return 0;
for(int i = A; i <= B; i++)
{
if((i % K) == 0)
{
noOfDivisors++;
}
}
return noOfDivisors;
}
If I understood the question correctly I believe this is the solution:
public static int solution(int A, int B, int K) {
int count = 0;
if(K == 0) {
return (-1);
}
if(K > B) {
return 0;
}
for(int i = A; i <= B; ++i) {
if((i % K) == 0) {
++count;
}
}
return count;
}
returning -1 is due to an illegal operation (division by zero)
int solution(int A, int B, int K) {
int tmp=(A%K==0?1:0);
int x1=A/K-tmp ;
int x2=B/K;
return x2-x1;
}
100/100 - another variation of the solution, based on Pham Trung's idea
class Solution {
public int solution(int A, int B, int K) {
int numOfDivs = A > 0 ? (B / K - ((A - 1) / K)) : ((B / K) + 1);
return numOfDivs;
}
}
class Solution {
public int solution(int A, int B, int K) {
int a = A/K, b = B/K;
if (A/K == 0)
b++;
return b - a;
}
}
This passes the test.
It's similar to "how many numbers from 2 to 5". We all know it's (5 - 2 + 1). The reason we add 1 at the end is that the first number 2 counts.
After A/K, B/K, this problem becomes the same one above. Here we need to decide if A counts in this problem. Only if A%K == 0, it counts then we need to add 1 to the result b - a (the same with b+1).
Here's my solution, two lines of Java code.
public int solution(int A, int B, int K) {
int a = (A == 0) ? -1 : (A - 1) / K;
return B / K - a;
}
The thought is simple.
a refers to how many numbers are divisible in [1..A-1]
B / K refers to how many numbers are divisible in [1..B]
0 is divisible by any integer so if A is 0, you should add one to the answer.
Here is my solution and got 100%
public int solution(int A, int B, int K) {
int count = B/K - A/K;
if(A%K == 0) {
count++;
}
return count;
}
B/K will give you the total numbers divisible by K [1..B]
A/K will give you the total numbers divisible by K [1..A]
then subtract, this will give you the total numbers divisible by K [A..B]
check A%K == 0, if true, then + 1 to the count
Another O(1) solution which got 100% in the test.
int solution(int A, int B, int K) {
if (A%K)
A = A+ (K-A%K);
if (A>B)
return 0;
return (B-A)/K+1;
}
This is my 100/100 solution:
public int solution1(int A, int B, int K) {
return A == 0 ? B / K - A / K + 1 : (B) / K - (A - 1) / K;
}
0 is divisible by any integer so if A is 0, you should add one to the answer.
This is the O(1) solution, ( There is no check required for the divisility of a)
public static int countDiv(int a, int b, int k) {
double l1 = (double)a / k;
double l = -1 * Math.floor(-1 * l1);
double h1 = (double) b / k;
double h = Math.floor(h1);
Double diff = h-l+1;
return diff.intValue();
}
There is a lot of great answers, but I think this one has some elegance in it, also gives 100% on codility.
public int solution(int a, int b, int k) {
return Math.floorDiv(b, k) - Math.floorDiv(a-1, k);
}
Explanation: Number of integers in the range [1 .. B] that divisible by K is B/K. Range [A .. B] can be transformed to [1 .. B] - [1 .. A) (notice that round bracket after A means that A does not belong to that range). That gives as a result B/K - (A-1)/K. Math.floorDiv is used to divide numbers and skip remaining decimal parts.
I will show my code in go :)
func CountDiv(a int, b int, k int) int {
count := int(math.Floor(float64(b/k)) - math.Floor(float64(a/k)));
if (math.Mod(float64(a), float64(k)) == 0) {
count++
}
return count
}
The total score is 100%
If someone is still interested in this exercise, I share my Python solution (100% in Codility)
def solution(A, B, K):
if not (B-A)%K:
res = int((B-A)/K)
else:
res = int(B/K) - int(A/K)
return res + (not A%K)
int divB = B / K;
int divA = A / K;
if(A % K != 0) {
divA++;
}
return (divB - divA) + 1;
passed 100% in codelity
My 100% score solution with one line code in python:
def solution(A, B, K):
# write your code in Python 3.6
return int(B/K) - int(A/K) + (A%K==0)
pass
int solution(int A, int B, int K)
{
// write your code in C++14 (g++ 6.2.0)
int counter = 0;
if (A == B)
A % K == 0 ? counter++ : 0;
else
{
counter = (B - A) / K;
if (A % K == 0) counter++;
else if (B % K == 0) counter++;
else if ((counter*K + K) > A && (counter*K + K) < B) counter++;
}
return counter;
}
Assumptions:
A and B are integers within the range [0..2,000,000,000];
K is an integer within the range [1..2,000,000,000];
A ≤ B.
int from = A+(K-A%K)%K;
if (from > B) {
return 0;
}
return (B-from)/K + 1;
I am wanting to ask the user to input three numbers and then have program calculate the GCD using Euclid's algorithm all the while using recursion.
My code right now implements two input numbers. I understand the approach of calculating the GCD of a and b, and calling it result d. Then using the third input (c) and d to find the GCD and essentially repeating Euclid's algorithm again; I am not sure how to implement this in code.
import java.util.Scanner;
public class RecursionDemo {
public static void main (String[] args) {
Scanner userInput = new Scanner(System.in);
System.out.println("Enter first number: ");
int a = userInput.nextInt();
System.out.println("Enter second number: ");
int b = userInput.nextInt();
System.out.println("GCD is: " + gCd(a, b));
}
public static int gCd(int a, int b) {
if(b == 0){
return a;
}
return gCd(b, a%b);
}
}
The part that is really throwing me off is using recursion to solve my problem.
So far I know I need to implement:
System.out.println("Enter third number: ");
int c = userInput.nextInt();
d = //Not sure here
//And then modify my recursion method to find GCD.
Any help or suggestions would greatly be appreciated!
d = gCd (a, b);
System.out.println("GCD is: " + gCd(d, c));
Note that you may call your gCd function with any two arguments, not just a and b. For better understanding and less confusion, you may want to rename its arguments, like the following:
public static int gCd(int x, int y) {
if(y == 0) {
return x;
}
return gCd(y, x%y);
}
So, first you call it with x = a and y = b to find GCD of a and b. Store the result into new variable d. After that, you call it again with x = d which is in turn GCD of a and b, and y = c. Thus you get the GCD of all the three numbers.
The gcd method can be iterated to obtain the gcd of a larger set of numbers.
For example:
gCd(a, b, c) = gCd( gCd(a, b), c)
and
gCd(a, b, c, d) = gCd( gCd(a, b, c), d) so then
gCd(a, b, c, d) = gCd( gCd( gCd(a, b), c), d)
Easy, specific solution:
System.out.println("GCD is: " + gCd( gCd(a, b), c) );
However, if you'll notice, there is recursion going on. I've created a method that takes an array of integers as an input. It will work for an array of size three, or any size. Here are the methods:
/* returns gcd of two numbers: a and b */
public static int gCd(int a, int b) {
if (b == 0) {
return a;
}
return gCd(b, a%b);
}
/* returns gcf of an array of numbers */
public static int gCd(int[] numbers)
{
int result = numbers[0]; // first number
for(int i = 1; i < numbers.length; i++) {
result = gCd(result, numbers[i]); // gcf of itself and next #
}
return result;
}
So, to relate it to your code:
Scanner userInput = new Scanner(System.in);
System.out.println("Enter first number: ");
int a = userInput.nextInt();
System.out.println("Enter second number: ");
int b = userInput.nextInt();
System.out.println("Enter third number: ");
int c = userInput.nextInt();
// you can do this
System.out.println("GCD is: " + gCd( gCd(a, b), c) );
// or you can do this
int[] numbers = {a, b, c};
int d = gCd(numbers);
System.out.println("GCD is: " + d);
Sample input/output:
Enter first number:
12
Enter second number:
18
Enter third number:
30
GCD is: 6
GCD is: 6