I want to take any user input integer between 1 and 9999 and return that number with its digits reversed. The problem with my code is it's returning the sum of the entered integer and I have no idea how to fix it. This is the code that that I came up with so far:
import java.util.Scanner;
class Reverse{
public static void main(String []args){
Scanner input = new Scanner(System.in);
System.out.print("Enter a number between 1 and 9999: ");
int user = input.nextInt();
if(user>1 && user<9999){
System.out.println("The number with its digits reversed is : " + reverseDigit(user));
}else{
System.out.println("Invalid Input");
}
}
public static int reverseDigit(int num){
return (num%10 + (num%100)/10 + (num%1000)/100 + num/1000); //This is the problem
}
}
You could replace :
return (num%10 + (num%100)/10 + (num%1000)/100 + num/1000);
with:
return ((num%10)*1000 + ((num%100)/10 )*100+ ((num%1000)/100)*10 + num/1000);
The reason that the first was wrong is because you get:
last digit:num%10
third digit:num%100)/10
second digit:(num%1000)/100
first digit:num/1000
so you was just adding all the digits before
But the Above works only for numbers from 1000-9999 .So you could replace the reverseDigit method with this simple method that works for every number:
public static int reverseDigit(int num){
int reverse=0;
while( num != 0 )
{
reverse = reverse * 10;
reverse = reverse + num%10;
num = num/10;
}
return reverse;
}
First, convert the number into a string then reverse the string and reconvert it into a number.
public static int reverseDigit(int num)
{
String str;
str = String.valueOf(num);
str = new StringBuilder(str).reverse().toString();
return (Integer.parseInt(str));
}
public static int reverseDigit(int num) {
int result = 0;
while(num != 0 ) {
result *=10;
int temp = num % 10;
result += temp;
num /=10;
}
return result ;
}
To do it using int (although String would be better).
public void test() {
System.out.println("Reversed: " + 1234 + " = " + reverseDigits(1234, 4));
}
public static int reverseDigits(int num, int digits) {
int reversed = 0;
for (int i = 0; i < digits; i++) {
reversed *= 10;
reversed += num % 10;
num /= 10;
}
return reversed;
}
Related
im trying to make a calculator and im was unable to continue because of some confusion in my codes. i was trying to make a factorial of a number, if its a positive number there is no error but every time i input a negative number it results to 1, here is my code .
import java.math.BigInteger;
import java.util.Scanner;
public class Factorial2 {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
System.out.print("Enter a number: ");
int n = s.nextInt();
String fact = factorial(n);
System.out.println("Factorial is " + fact);
}
public static String factorial(int n) {
BigInteger fact = new BigInteger("1");
for (int i = 1; i <= n; i++) {
fact = fact.multiply(new BigInteger(i + ""));
}
return fact.toString();
}
}
i already tried making if statements but still it results to 1.i also want to make the negative factorial into a display text not the value of the negative factorial
You need to validate the input before the calculation, example:
public static String factorial(int n) {
if(n < 1) return "0";
BigInteger fact = new BigInteger("1");
for (int i = 1; i <= n; i++) {
fact = fact.multiply(new BigInteger(i + ""));
}
return fact.toString();
}
Of course you can define any default return value or throw an error:
if(n < 1) throw new RuntimeException("Input must be > 0");
I know how to code to find the factorial of a number:
public static void factorialcalculations()
{
int usernumber, calculation, fact = 1;
System.out.println("Enter an integer to calculate it's factorial");
Scanner in = new Scanner(System.in);
usernumber = in.nextInt();
if ( usernumber < 0 )
System.out.println("Number should be non-negative.");
else
{
for ( calculation = 1 ; calculation <= usernumber ; calculation++ )
fact = fact*calculation;
System.out.println("Factorial of "+usernumber+" is = "+fact);
{
But what I need is for is to display what numbers it is being multiplied by for example if it was 5
I need it to display the factorial is: 5*4*3*2*1=120
Use recursion. The value you want to display for n=1 is "1=". For any other n, it's "n*" + display(n-1).
display(2) => "2*" + display(1) => "2*1="
display(3) => "3*" + display(2) => "3*2*1="
and so on.
There is lot of ways to do it. With your existing code you can print it within your existing loop. Recursive will be the elegant way to find the factorial.
public static int factorial(int n) {
System.out.print("factorial is : ");
int result = 1;
for (int i = n; i >= 1; i--) {
result = result * i;
System.out.print(i!=1 ? (i+"*"): (i+"="));
}
System.out.println(result);
return result;
}
PS: As a best practice you need to handle the all scenarios in here. (String/negative/.. inputs)
Here is what you seem to be looking for man:
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the number whose factorial is to be found: ");
int n = scanner.nextInt();
int result = factorial(n);
System.out.println(getFactString(n,result));
}
public static int factorial(int n) {
int result = 1;
for (int i = 1; i <= n; i++) {
result = result * i;
}
return result;
}
public static String getFactString(int n, int result){
String output= "";
int count = n;
for (int i = count; i > 0; i--) {
if (n==1) {
output = output + n +" = ";
break;
}
output = output + n+" * ";
n--;
}
return output + result;
}
It's also possible to do this will StringBuilder as well. With the getFactorString() method, it doesn't matter what n is, you will get the correct string returned to display.
I am trying to use a set to find the unique numbers and get the sum from user entered numbers. I heard that arrays are easier but a set might just do for me. I don't know much about sets or what they do so any input would be fantastic. Much appreciated everybody!
import java.util.Scanner;
public class getdistinct
{
int dialr;
Scanner scan = new Scanner(System.in);
public double go()
{
double a = 0
counter = 10;
int total = 0;
for (counter != 0)
{
int thisisnewnumber = scan.nextInt();
System.out.println("Enter number that you want to add: ");
if(newInteger < 0)
{
n = n + 1
dial = dial - 1;
}
else
{
System.out.println("wrong");
}
}
System.out.println("the total is ";
return a;
}
}
java.util.HashSet stores unique values. Made minor changes to your program to use Set to store unique values and calculate sum of unique values using for loop
import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;
public class quiz_assignment {
int counter;
Scanner scan = new Scanner(System.in);
public int go() {
int a = 0;
int n = 0;
counter = 10;
Set<Integer> unValues = new HashSet<Integer>();
while (counter != 0) {
System.out.println("Enter Integer: ");
int newInteger = scan.nextInt();
if (newInteger < 0) {
unValues.add(new Integer(newInteger));
n += newInteger;
counter = counter - 1;
a = a + newInteger;
} else {
System.out
.println("Must be negative integer, please try again");
}
}
int unSum = 0;
for (Integer value : unValues) {
unSum += value;
}
System.out.println("The sum of all ten integers is: " + a);
System.out.println("The sum of unique integers is: " + unSum);
return n;
}
public static void main(String[] args) {
quiz_assignment o = new quiz_assignment();
o.go();
}
}
Set has its implementation in various classes like HashSet, TreeSet, LinkedHashSet. Following is an example to explain Set functionality
I used here (HashSet).
import java.util.Scanner;
public class quiz_assignment
{
int counter;
Scanner scan = new Scanner(System.in);
Set<Integer> ditinctSet = new HashSet<Integer>();
public int go()
{
int a=0;
int n=0;
counter = 10;
int total = 0;
while (counter != 0)
{
System.out.println("Enter Integer: ");
int newInteger = scan.nextInt();
if(!ditinctSet.contains(newInteger)){
ditinctSet.add(newInteger);
}
if(newInteger < 0)
{
n+=newInteger;
counter = counter - 1;
a=a+newInteger;
}
else
{
System.out.println("Must be negative integer, please try again");
}
}
System.out.println("The sum of all ten integers is: " + a);
System.out.println("Distinct numbers are: ");
System.out.println(ditinctSet);
return n;
}
}
And here a link to start knoing more about sets.
Hashsets are useful because they don't store duplicate entries. You can use them to store your set of unique numbers that the user inputs. I also removed the variable "a" from your code because its purpose seemed identical to variable n's.
import java.util.Scanner;
public class quiz_assignment{
int counter;
Scanner scan = new Scanner(System.in);
public int go()
{
HashSet<Integer> distinctNumbers = new HashSet<>();
int n=0;
counter = 10;
int total = 0;
while (counter != 0)
{
System.out.println("Enter Integer: ");
int newInteger = scan.nextInt();
if(newInteger < 0)
{
n+=newInteger;
counter = counter - 1;
distinctNumbers.add(newInteger);
}
else
{
System.out.println("Must be negative integer, please try again");
}
}
int size = distinctNumbers.size();
System.out.println("The sum of all ten integers is: " + n);
System.out.println("You inputed " + size + " numbers.");
System.out.println("Your numbers are:");
for(Integer i: distinctNumbers){
System.out.println(i);
}
return n;
}
}
I am going to post my code below because this is kind of hard to describe. The code below works, but it is using Math.pow in the main method rather than in the helper, so if someone could show me a way to move the power to the helper method without messing up the program that would be much appreciated.
Main method:
Scanner keyboard = new Scanner(System.in);
System.out.println("Please enter an integer: ");
double input = keyboard.nextInt();
double x = Math.pow(2.0, input);
int n = (int)x;
System.out.println(starStr(n));
Helper method:
public static String starStr(int n)
{
if (n >= 1) {
return ("*" + starStr(n-1));
}
else {
return "";
}
}
EDIT:
if(n == 0) {
return "*";
}
else {
return starStr(n - 1) + "**";
}
Something like this would work. You don't really need to use a power function at all. Just start with 1 star and double the number of stars in every step of the recursion.
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
System.out.println("Please enter an integer for the number of stars: ");
int input = keyboard.nextInt();
System.out.println(doStars(input));
}
public static String doStars(int n)
{
//If n == 0 the recursion is done
//Otherwise, reduce n by 1 and double the number of stars
if(n == 0)
return "*";
else
{
String output = doStars(n - 1);
return output + output;
}
}
I think this is what you are looking for. Not sure if you have learned the tree data-structure, but that's the purpose of my variable names.
public class Main {
public static void main(String[] args) {
for (int i = 0; i < 5; i++) {
// 1 + (2^n)-1 = 2^n
System.out.println("*" + doStars(i));
}
}
public static String doStars(int n)
{
if (n == 0) {
return "";
}
else {
String subTree = doStars(n - 1);
return subTree + "*" + subTree; // length = (2^n)-1
}
}
}
Output
*
**
****
********
****************
Visualization - read clockwise in triangles from little to big
"*"
+
doStars(2)
"*"
doStars(1) + doStars(1)
"*" "*"
doStars(0) + doStars(0) doStars(0) + doStars(0)
"" "" "" ""
Note: Just a practice problem, not for marks.
This is a practice problem given in a first year Java course:
Design and implement an application that reads an arbitrary number of integers, by the user, that are in the range 0 to 50 inclusive, and counts how many occurrences of each are entered. After all the input has been processed, print all of the values (with the number of occurrences) that were entered one or more times.
In addition, write a method that returns no value which would compute the average of the occurrences of all numbers entered by the user.
This is what I have (I have skipped the "average occurrence" part until I clean this up):
import java.util.Scanner;
public class Main
{
public static Scanner scan = new Scanner(System.in);
public static int[] userIntegers() // this method will build the array of integers, stopping when an out-of-range input is given
{
System.out.println("Enter the number of integers to be recorded: ");
int numInts = scan.nextInt();
int[] userArray = new int[numInts];
int i = 0;
while(i < numInts)
{
System.out.println("Enter an integer between 1-50 inclusive: ");
int userInteger = scan.nextInt();
if(isValidInteger(userInteger))
{
userArray[i] = userInteger;
i++;
}
else if(isValidInteger(userInteger) == false)
{
System.out.println("Try again.");
}
}
return userArray;
}
public static void occurrenceOutput(int[] input) // this method will print the occurrence data for a given array
{
int[] occurrenceArray = new int[51];
int j = 0;
while(j < 51) // iterates through all integers from 0 to 50, while the integer in the array is equal to integer j, the corresponding occurance array element increments.
{
for(int eachInteger : input)
{
occurrenceArray[j] = (eachInteger == j)? occurrenceArray[j]+=1: occurrenceArray[j];
}
j++;
}
int k = 0;
for(int eachOccurrence : occurrenceArray) // as long as there is more than one occurrence, the information will be printed.
{
if(eachOccurrence > 1)
{
System.out.println("The integer " + k + " occurrs " + eachOccurrence + " times.");
}
k++;
}
}
public static boolean isValidInteger(int userInput) // checks if a user input is between 0-50 inclusive
{
boolean validInt = (51 >= userInput && userInput >= 0)? true: false;
return validInt;
}
public static void main(String[] args)
{
occurrenceOutput(userIntegers());
}
}
Can someone point me in a more elegant direction?
EDIT: Thanks for the help! This is where I am at now:
import java.util.Scanner;
public class simpleHist
{
public static void main(String[] args)
{
getUserInputAndPrint();
getIntFreqAndPrint(intArray, numberOfInts);
}
private static int numberOfInts;
private static int[] intArray;
private static int[] intFreqArray = new int[51];
public static void getUserInputAndPrint()
{
// The user is prompted to choose the number of integers to enter:
Scanner input = new Scanner(System.in);
System.out.println("Enter the number of Integers: ");
numberOfInts = input.nextInt();
// The array is filled withchInteger = integer; integers ranging from 0-50:
intArray = new int[numberOfInts];
int integer = 0;
int i = 0;
while(i < intArray.length)
{
System.out.println("Enter integer value(s): ");
integer = input.nextInt();
if(integer > 50 || integer < 0)
{
System.out.println("Invalid input. Integer(s) must be between 0-50 (inclusive).");
}
else
{
intArray[i] = integer;
i++;
}
}
// Here the number of integers, as well as all the integers entered are printed:
System.out.println("Integers: " + numberOfInts);
int j = 0;
for(int eachInteger : intArray)
{
System.out.println("Index[" + j + "] : " + eachInteger);
j++;
}
}
public static void getIntFreqAndPrint(int[] intArray, int numberOfInts)
{
// Frequency of each integer is assigned to its corresponding index of intFreqArray:
for(int eachInt : intArray)
{
intFreqArray[eachInt]++;
}
// Average frequency is calculated:
int totalOccurrences = 0;
for(int eachFreq : intFreqArray)
{
totalOccurrences += eachFreq;
}
double averageFrequency = totalOccurrences / numberOfInts;
// Integers occurring more than once are printed:
for(int k = 0; k < intFreqArray.length; k++)
{
if(intFreqArray[k] > 1)
{
System.out.println("Integer " + k + " occurs " + intFreqArray[k] + " times.");
}
}
// Average occurrence of integers entered is printed:
System.out.println("The average occurrence for integers entered is " + averageFrequency);
}
}
You are actually looking for a histogram. You can implement it by using a Map<Integer,Integer>, or since the range of elements is limited to 0-50, you can use an array with 51 elements [0-50], and increase histogram[i] when you read i.
Bonus: understanding this idea, and you have understood the basics of count-sort
To calculate occurences, you can do something like this:
for(int eachInteger : input) {
occurrenceArray[eachInteger]++;
}
This will replace your while loop.