I need to find the smallest number which digit numbers product is equal to a given num.
import java.util.Scanner;
class timus_1014_2 {
public static void main(String[] args){
int[] arr = new int[10]; // eskan ban# chem imanum inchi a statik,
int prod = 1;
int j = 0;
Scanner in = new Scanner(System.in);
int n = in.nextInt();
for (int i = 2; i < 10; ++i){
if (n % i == 0) {
arr[j] = i;
j++;
}
}
prod = prod * arr[j];
System.out.print(prod);
}
}
Something is wrong with the logic, whats is the problem when I input 10 it should give 25 but it gives 0. Please give ideas of how to make a program find a number which digits product is a given num.
If I understood your problem correctly you need a number whose product of digits equals a number N. Since you asked for new algorithm , you can chck following code.
Logic:
Note : For number whose prime factors are less than 10
Get all factors from 9 -> 2
add to list
print in reverse or use stack instead of list
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
class Main {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.println("Enter number");
int num = in.nextInt();
List<Integer> lst = new ArrayList<>();
for (int p = 9; p >= 2; p--) {
while (num % p == 0) {
num /= p;
lst.add(p);
}
}
String smallestNumber = "";
for (int i = lst.size() - 1; i >= 0; i--) {
smallestNumber = smallestNumber + lst.get(i);
}
System.out.println("Smallest number : " + smallestNumber);
}
}
Output :
Enter number
10
Smallest number : 25
Enter number
144
Smallest number : 289
Enter number
12
Smallest number : 26
I suggest you look at each error is fix it one by one. I also suggest you use an IDE which will show you the errors and you type and will help ensure you don't have an overwhelming number of errors and you can see if those error disappear based on your corrections.
BTW Often when you use an array for a short piece of code, it can often be eliminate as I suspect it can be removed in your case.
Static methods can not access non-static members of class.
In your case prod is member variable of class but not static. To fix the error , try to make prod as static.
private static int prod = 1;
I would prefer , to make it local variable if no other method is using it.
The problem here is you need to create an object of the particular class to call a particular method associated with it
import java.util.Scanner;
class DigPro {
static int[] arr = new int[10]; // eskan ban# chem imanum inchi a statik,
int prod = 1;
public static void main(String[] args){
Scanner in = new Scanner(System.in);
DigPro obj = new DigPro();
obj.prime(in.nextInt());
}
public void prime(int n){
for (int i = 1; i < 10; ++i){
for (int j = 0; j < 9; ++j) {
if (n % i == 0) {
arr[j] = i;
}
prod = prod * arr[j];
}
}
System.out.print(prod);
}
}
Here you need to create an object say obj of DigPro class and then call prime(int n) method with that object. Also your division is startint with zero which is changed to one
In above code you are increasing j after the assigning value to arr[j].You should do the following:-
prod = prod * arr[j-1];
Here it will multiply prod with last array updated. That is why you are getting zero. And for your another question find the smallest number which digit numbers product is equal to a given num has similar answer at this link.
Since this is actually a pretty interesting problem, I took the time to come up with a correct solution for all possible integer inputs.
import java.util.*;
public class Main{
public static void main(String[] args) {
System.out.println("Enter number:");
int number = new Scanner(System.in).nextInt();
Stack<String> factors = new Stack<>();
if(number==0){
factors.push("0");
}else if(number==1){
factors.push("1");
}else{
for(int f=9;f>1;f--){
while(number%f==0){
factors.push(Integer.toString(f));
number/=f;
}
}
}
if(number<0){
factors.push("-");
}
if(number>9){
System.out.println("This is impossible.");
}else{
System.out.println("Smallest Number:");
while(!factors.empty()) System.out.print(factors.pop());
}
}
}
Related
This question already has answers here:
Int division: Why is the result of 1/3 == 0?
(19 answers)
Closed last year.
I want to find the sum using basic loops, so I used the following code:
// sum of first n terms in the series, 1 - 1/1! + 2/2! - 3/3!...
package assignment02;
import java.util.Scanner;
public class P7Bnew {
public static void main(String[] args) {
Scanner in = new Scanner (System.in);
System.out.println("Enter number of terms.");
int n = in.nextInt();
// using for loop to find sum
double sum =1;
for (int i =1; i<n ; i++)
{
int fact = 1;
for (int j=1; j<=i; j++)
{
fact *= i;
}
if (i%2==0)
sum+= ((int)i/fact);
else
sum -= ((int)i/fact);
}
System.out.println("The sum of first "+n+ " terms is "+sum);
}
}
I want to restrict from using the predefined functions.
In this way I am getting sum as 1 for n>=4.
So I tried another way for alternately adding and subtracting terms from :
import java.util.*;
import java.lang.*;
import java.io.*;
class P7B
{
public static void main (String[] args) throws java.lang.Exception
{
Scanner in = new Scanner (System.in);
int a = in.nextInt();
double sum = 1;
for (int i=1; i<a ; i++)
{
int fact=1;
for (int j=2; j<=i;j++)
{
fact = fact * j;
}
int sign;
if ((i%2)==0)
sign =1;
else
sign = -1;
sum = (sum + (sign*(i/fact)));
}
System.out.println("The sum of the first "+a+ " terms of the series 1 - (1/1!) + (2/2!) - (3/3!)... is "+(sum)+".");
}
}
But I got same results.
Later when I used Math.pow(-1, i) instead of the sign variable, it gave me the correct result.
Please tell me the reason my initial attempts were giving incorrect sum for n>=4.
Your problem is that in i/fact as well as in (sign*i)/fact all operands are ints and thus you will get 0 as the result of that calculation (1/2 etc. is 0 in integer math and so will be i/i! with the exception of 1/1!and 2/2! because that's just 1/1 and 2/2). When using Math.pow(-1,i) you get a double and now the calculation works.
So to fix your code use a cast to double:
if (i%2==0)
sum += (double)i/fact;
else
sum -= (double)i/fact;
Assume, you input the number 546, then you should find the product of its digits, which is 546=120, then multiply the digits of 120 until and so on, continue until you get a one digit number.
Here's the code I wrote, but the loop doesn't work correctly and I've tried to fix it, but nothing changed. Could you please help me?
import java.util.*;
public class Product {
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
int a = keyboard.nextInt();
System.out.println("Please input the number");
numberOfProducts(a);
}
public static void numberOfProducts(int n){
int product = 1;
while(n>10) {
int current = n;
while (current != 0) {
product = product * (current % 10);
current = current / 10;
n = product;
System.out.println(product);
}
}
}
}
For a different take on the solution you can use a recursive lambda
import java.util.Scanner;
import java.util.function.IntFunction;
public class Product {
// this simply reduces the number to the product of its digits.
static IntFunction<Integer> prod =
(a) -> a < 10 ? a : a % 10 * Product.prod.apply(a / 10);
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
System.out.print("Please input the number");
int n = keyboard.nextInt();
// Now continue applying the lambda until the result is < 10.
while (n > 10) {
n = prod.apply(n);
}
System.out.println(n);
}
}
I think you are looking something like the code below:
import java.util.Scanner;
public class Main {
public static int numberOfProducts(String number) {
int product = 1;
do {
for (int i = 0; i < number.length(); ++i){
// This line converts the every digit of the number string to an integer.
product *= number.charAt(i) - '0';
}
// Remove this line, if you don't want to print the product of each iteration.
System.out.println(number);
// Update number with the new product.
// This line converts the int product to a new string.
number = "" + product;
} while (product > 10);
return product;
}
public static void main(String[] args) {
System.out.print("Please input the number: ");
Scanner keyboard = new Scanner(System.in);
int a = keyboard.nextInt();
// Treat number as a string for easier indexing.
String number = "" + a;
System.out.println(numberOfProducts(number));
}
}
When the above code runs, with 546 as input, it outputs:
Please input the number: 546
546
120
0
After looking through your code, your issue seems to be in this expression:
current % 10.
The modulo operation gives you the remainder of a division by ten.
In the case of your input 120, the result of that operation would be 0.
Following the rest of your application logic, your iteration variable will be set to zero, ending your loop immediately.
I will not give you copy-paste code to fix this problem, as it seems like a programming course assignment. I will however help you solve it.
My suggested fix is to change your approach to this problem and not try to solve this the mathematical way, but rather in a way that takes advantage of the Java programing language.
You could change your input from an Integer to a String.
In which case, you can use String.length() to ensure your requirement is fulfilled when exiting the loop.
In your loop, you split the String into substrings of length 1. Afterwards, you just multiply these.
When the loop exits (because String length is no longer greater than 1) you will have your intended result.
Good luck!
Actually your code is very close to being correct, the only thing you're doing wrong is that you are not resetting the product variable between iterations. You simply need to move the int product = 1; instruction inside the outer while loop.
Also, if you want a single digit at the end, your condition should be while(n >= 10) or while(n > 9), since 10 is still 2 digits, so we need one more iteration !
Final remark: sometimes it's easier to break your code into smaller pieces. It is easier to understand and easier to test/debug ! For example you could have first created a function productOfDigits(n) that returns the result of a single iteration, and then another function productOfDigitsUntilSingleDigit(n) that repeatedly calls the previous function.
import java.util.*;
public class Product {
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
int a = keyboard.nextInt();
System.out.println("Please input the number");
numberOfProducts(a);
}
public static void numberOfProducts(int n){
int product = 1;
while (n != 0) {
product = product * (n % 10);
n = n / 10;
}
if(product > 10) {
System.out.println("Intermediate result="+product);
numberOfProducts(product);
}
else
System.out.println("Final 1 digit product="+product);
}
}
function getProductUntilSingleDigit(n) {
let product = 1;
while (n > 0 || product > 9) {
if (n == 0) {
n = product;
product = 1;
}
product = product * (n % 10);
n = Math.floor(n / 10);
}
return product;
}
console.log(getProductUntilSingleDigit(546));
I received that task:
"A small method, calculateProduct is to be written. It will ask the user to enter two int values, and then calculate and display the product of all the values between the two values entered. For example if the user enters the numbers 2 and 5 the program will display the result 120 (calculated as 2 * 3 * 4 * 5)"
I tried to build something like this:
import java.util.Scanner;
public class Exam {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int a;
int b;
int big;
int small;
//ask to insert two variables
System.out.println("Insert variable a");
a = in.nextInt();
System.out.println ("Insert variable b");
b=in.nextInt();
// compare two variables
// set the biggest variables to b, the smallest - to a
if (a >=b){
big=a;
small=b;
}
else {
big=b;
small=a;
}
// set the do while loop to complete the code. Run multiplying before counter won't fit to b variable
int result = small;
for (int i=small; i<=big;i++){
result*=i;
}
System.out.println("the multiplication progression between "+small+" and "+big+" equals to "+result);
}
}
However, when I insert 2 and 5 the result is 240. Does anybody know how to fix it? thanks!
Change loop to:
for (int i = small + 1; i <= big; i++)
{
result *= i;
}
you init result with small then multiply it by small again.
Fix: Start the for statement with small+1
...
int result = small;
for (int i=small+1; i<=big;i++){
result*=i;
}
....
The other obvious solution here is to change the init statement from
int result = small;
to
int result = 1;
In that case you don't have to touch your looping code.
And for the record: "small" is a rather bad name here, why not call it "smallerInput" or something like that.
Finally: you could avoid dealing with "small" - if a < b you can simply loop from a to b; and otherwise you could loop "backwards" from "b to a".
Just change your for loop as below mentioned will solve your problem.
The problem in your loop is :
In its first iteration it is multiple with itself rather than its
incremented value.
From:
for (int i=small; i<=big;i++)
To:
for (int i=small+1; i<=big;i++)
The task is to write a method called "calculateProduct". Above you are doing all your callculation in your main method. Try to separate that. Example :
import java.util.Scanner;
public class Exam {
public static void main (String[]args) {
Scanner in = new Scanner(System.in);
int a;
int b;
System.out.println("Insert variable a");
a = in.nextInt();
System.out.println ("Insert variable b");
b=in.nextInt();
if(a>=b){
calculateProduct(b,a);
}
else{
calculateProduct(a,b);
}
}
public static void calculateProduct (int m, int n) {
int result = 1;
for (int i = m; i <= n; i++) {
result *= i;
}
System.out.println("the multiplication progression between "+m+" and "+n+" equals to "+result);
}
}
My question is why isn't the code generating the amount of numbers that the users enters? Right now the code is only generating one number. Here is the original question given to me:
"In your main method, prompt the user for a number n. Write a method
called assessRandomness that generates a random number between 1 and
100 'n' times and return the percentage of times the number was less than
or equal to 50. Call your assessRandomness method from main and display
the result to the user from main. Do not interact with the user from
within the assessRandomness method."
output:
How many random numbers should I generate? 10
<assume the random numbers generated were 11 7 50 61 52 3 92 100 81 66>
40% of the numbers were 50 or less
my code:
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.println("how many random numbers should I generate?: ");
int number = in.nextInt();
assessRandomness(number);
}
public static double assessRandomness(int n){
int random = (int)(Math.random()*100);
int randomNumbersLessthan50 = 0;
if (random <= 50)
{
double getPercentage = random/randomNumbersLessthan50;
}
else
{
System.out.println(random);
}
return random;
}
I don't see any kind of loop within assessRandomness.
Try
for(int x = 1; x <= n; x++){ ... }
as first line in assessRandomness, it should finally look like
public static double assessRandomness(int n){
int counterLessThan50 = 0;
for ( int x = 1; x <= n; x++)
if( (int)(Math.random()*100) <= 50 ) counterLessThan50++;
return (double) counterLessThan50 / n;
}
There's no repetition in your code to do something n times.
Here's one way to do it in one line using a stream:
public static double assessRandomness(int n) {
return Stream.generate(Math::random).limit(n).map(r -> r * 100 + 1).filter(r -> r <= 50).count() / (double)n;
}
Note that converting Math.random() to a number in the range 1-100 is pointless; this will give the same result:
public static double assessRandomness(int n) {
return Stream.generate(Math::random).limit(n).filter(n -> n < .5).count() / (double)n;
}
And is easier to read.
At the moment, your assessRandomness method never uses the variable n.
At first you should initialize a variable which counts the number of created randoms that are bigger than 50 (this will be your retutn value). You should then do a loop from 0 until n. For each loop run you should create a random value between 0 and 100. Then you should check wether the value is bigger than 50. If so, count up your previously created variable. When the loop has finished, return the count variable and print it in the main method.
This should help you understand better how to do something like this.
public static void main(String[] args) {
System.out.println("how many random numbers should I generate?: ");
Scanner in = new Scanner(System.in);
int number = in.nextInt();
int[] arrayPlaceHolderInMainMethod = new int[number];
arrayPlaceHolderInMainMethod = generateRandomNumberArray(number);
assessRandomness(arrayPlaceHolderInMainMethod);
}
public static void assessRandomness(int[] inputArray) {
int randomNumbersLessthan50 = 0;
int randomNumbersGreaterthan50 = 0;
int random = 0;
for (int i = 0; i < inputArray.length; i++) {
random = inputArray[i];
}
if (random <= 50) {
randomNumbersLessthan50 += 1;
} else {
randomNumbersGreaterthan50 += 1;
}
System.out.println(">50: " + randomNumbersGreaterthan50 + " Less: " + randomNumbersLessthan50);
}
public static int[] generateRandomNumberArray(int numberPickedByUser) {
int[] arrayOfRandomNumbers = new int[numberPickedByUser];
for (int i = 0; i < numberPickedByUser; i++) {
arrayOfRandomNumbers[i] = (int) (Math.random() * 100 + 1);
}
return arrayOfRandomNumbers;
}
I've written this little program to find n!:
public class Fattoriale {
public static void main (String[] args){
int n;
do {
n = Input.readInt("Enter an int number ( int >=0)");
while( n < 0);
long fatt = 1;
for (int i = 2; i <= n; i++){
fatta = fatt * i;
}
System.out.println(n"+!" + " = " + fatt);
Now I'm trying to rewrite this program using BigInteger. I've written this:
import jbook.util.*;
import java.math.*;
public class Fattoriale {
public static void main (String[] args){
String s = Input.readString("Enter an int number. ");
BigInteger big = new BigInteger(s);
BigInteger tot = new BigInteger("1");
BigInteger i = new BigInteger("2");
for (; i.compareTo(big) < 0; i.add(BigInteger.ONE)){
tot = tot.multiply(i);
}
System.out.println(tot);
}
}
But this program with BigInteger makes a loop and I can't understand why. I hope somebody can help me. Thank you very much ;). (nb. ignore Input class, it's only a class that I created to enter input faster)
This should be like this because i.add(BigInteger.ONE) doesn't update the variable i.
for (; i.compareTo(big) <= 0; i=i.add(BigInteger.ONE)) {
tot = tot.multiply(i);
}
There are two changes:
It should be <=0 instead of <0
Assign it back to i to update it.
How to confirm?
BigInteger i = new BigInteger("2");
System.out.println(i.add(BigInteger.ONE)); // print 3
System.out.println(i); // print 2
BigInteger is immutable, so unless you set a new value for it using the = operator, its value doesn't change. Thus, each time in the loop that you call i.add(BigInteger.ONE), the computer calculates i+1 and then throws away the result. Instead, try:
for (; i.compareTo(big) < 0; i=i.add(BigInteger.ONE)){