Develop Reference

Need help understanding this basic challenge?

Currently doing a challenge called number to words, I have created 2 methods, one which
deals with comparing values individually so that it can print out it's string value(method called numberToWord), another method called reverse which basically re-orders the values so that it is printed in a correct sequence, for example:s
Step One 567 --> Step 2, it will be converted into 765 --> Step 3, reverse method will then convert it back to 5,6,7 individually so that it can compare the values with the if statements. However, i have tried so many things to getting this to work, i managed to make it to step 3 but when i try to return the value it gives me 3 random values before it converts e.g = 7,6,7...5,6,7, i am unable to figure out how to remove the first 3 values and return just the last three values so that it can be compared in the numberToWords method.
package com.company;
public class Main {
public static void main(String[] args) {
numberToWords(567);
}
public static void numberToWords(int number) {
int lastDigit = 0;
int digit = number;
int reverseDigit = 0;
if (number < 0) {
System.out.println("Invalid Value");
}
for (int i = 0; i < digit; i++) {
//so we are taking the last digit from 567 per iteration
lastDigit = digit % 10;
//we are then dividing the digit by 10 each time so we can get another last digit
digit /= 10;
//i will now try to essentially get down to the final number which will be flipped
reverseDigit = (reverseDigit * 10) + lastDigit;
//checking values
System.out.println(reverse(reverseDigit));
// if (reverse(reverseDigit)== 0) {
// System.out.println("Zero");
// } else if (reverse(reverseDigit) == 1) {
// System.out.println("One");
// }else if (reverse(reverseDigit) == 2) {
// System.out.println("Two");
// }else if (reverse(reverseDigit) == 3) {
// System.out.println("Three");
// }else if (reverse(reverseDigit) == 4) {
// System.out.println("Four");
// }else if (reverse(reverseDigit) == 5) {
// System.out.println("Five");
// }else if (reverse(reverseDigit) == 6) {
// System.out.println("Six");
// }else if (reverse(reverseDigit) == 7) {
// System.out.println("Seven");
// }else if (reverse(reverseDigit) == 8) {
// System.out.println("Eight");
// }else if (reverse(reverseDigit) == 9) {
// System.out.println("Nine ");
// }
if (lastDigit == 0) {
System.out.println("Zero");
} else if (lastDigit == 1) {
System.out.println("One");
} else if (lastDigit == 2) {
System.out.println("Two");
} else if (lastDigit == 3) {
System.out.println("Three");
} else if (lastDigit == 4) {
System.out.println("Four");
} else if (lastDigit == 5) {
System.out.println("Five");
} else if (lastDigit == 6) {
System.out.println("Six");
} else if (lastDigit == 7) {
System.out.println("Seven");
} else if (lastDigit == 8) {
System.out.println("Eight");
} else if (lastDigit == 9) {
System.out.println("Nine");
}
}
}
public static int reverse (int a){
int lastDigit = 0;
for (int i =0; i < a; i++) {
lastDigit = a % 10;
a /= 10;
//testing values here
//System.out.println(lastDigit);
//sout in loop gives us 567
}
return lastDigit;
}
}

If I understand what you need correctly, you don't need that much code. Just print the reminder of division by 10 and then divide by ten for then next iteration until you get zero.
enum Numbers {
Zero,
One,
Two,
Three,
Four,
Five,
Six,
Seven,
Eight,
Nine;
}
private static void process(int number) {
do {
final int digit = number % 10;
System.out.println(Numbers.values()[digit]);
number /= 10;
} while (number > 0);
}
First use an enum since you can use it like an array but easier to declare. Then with the number you get, first get the reminder over ten. For any integer expressed as decimal the reminder over ten is the last digit. Since you have to print the last digit in the first place, just print it. Then replace number with number divided by ten. That will discard the last digit (the one just printed out) because this is an integer division. I mean, 1234 over 10 is 123.4 but because these are integer it gets truncated to 123. So now loop and the last digit will be printed again (but now it will be the first to the left due to the division). At some point, after printing the first digit of the original number you will have a one digit integer (i.e. 7) divided by ten which results in zero (because it would be 0.7 but it's an integer division).
You need to add some preconditions like the negatives.

I think you have the right idea of doing remainder division for numberToWords() and reverse().
But I think you're condition for exiting the for loop is wrong
for (int i = 0; i < digit; i++)
It will exit before you get all the digits. You want to loop until digit is 0, since you want to remainder divide UNTIL there's no more to divide ( meaning digit is 0).
so
for(int i = 0; digit != 0; i++){
...
}
while loop might be better than a for a loop since you're not using i anyways.
while(digit != 0){
...
}
It also depends on which IDE you're using but IntelliJ and eclipse can do a line by line debug so you see which line is causing issues.

How to print an int with comma divisors using a recursive method (no strings)?

In my computer science class, we were assigned a lab on recursion in which we have to print out a number with commas separating groups of 3 digits.
Here is the text directly from the assignment (the method has to be recursive):
Write a method called printWithCommas that takes a single nonnegative
primitive int argument and displays it with commas inserted properly.
No use of String.
For example printWithCommas(12045670); Displays 12,045,670
printWithCommas(1); Displays 1
I am really stumped on this. Here is my code so far:
public static void printWithCommas(int num) {
//Find length
if (num < 0) return;
int length = 1;
if (num != 0) {
length = (int)(Math.log10(num)+1);
}
//Print out leading digits
int numOfDigits = 1;
if (length % 3 == 0) {
numOfDigits = 3;
}
else if ((length+1) % 3 == 0) {
numOfDigits = 2;
}
System.out.print(num / power(10,length-numOfDigits));
//Print out comma
if (length > 3) {
System.out.print(',');
}
printWithCommas(num % power(10,length-numOfDigits));
}
It gets a stack overflow (which I can fix later), but it fails to print out some of the zeros, specifically the ones that are supposed to be after each comma.
I feel like I am taking this on with a completely wrong approach, but can't think of a good one. Any help would be appreciated.
Thanks in advance!
Note: power is a function I made that calculates power. First argument is the base, second is the exponent.

Here is the code I came up with, for anyone else that might be stuck on this:
public static void printWithCommas(int num) {
if (num > 999) {
printWithCommas(num/1000);
System.out.print(',');
if (num % 1000 < 100) System.out.print('0');
if (num % 1000 < 10) System.out.print('0');
System.out.print(num%1000);
}
else {
System.out.print(num);
}
}

Calculating how far a robot will move in Java

I'm working on a project for school that requires me to move a robot. How far the robot will move each second (variable t) is calculated by the function below.
The first function is easy. The 2nd and 3rd on the other are where I'm stuck. How would I write F(t-1)? Below is what I have so far.
if (t == 0) {
distance = 2;
} else if (t > 0 && <=6 || t > 12) {
// No clue on how to write the 2nd distance equation.
} else if (t >= 7 && <=12) {
// No clue on how to write the 3rd distance equation.
}

Recursion really isn't necessary to solve this.
Note that in each of the non-zero time cases, F(t) = F(t-1) + something.
So you can simply do:
double f = 2; /* Initial value at t=0 */
for (int t = 1; t <= maxT; ++t) { // maxT is the maximum value of t.
if (t <= 6 || t > 12) {
f += /* something for case 2 */;
} else {
f += /* something for case 3 */;
}
}
System.out.println(f);
You can do this with recursion, but you will get a StackOverflowError if maxT becomes modestly large; by contrast, using a loop will work for arbitrarily large maxT (modulo floating point errors).
As pointed out by #Andreas, you can do this without looping over all values of t:
double f = 2 * (maxT + 1);
for (int t = 7; t <= maxT && t <= 12; ++t) {
f += log(t) - 2;
}
and you can eliminate that loop too by precomputing the values.

This is a problem which involves the use of recursion. By and large, pay close attention to the notation Ft-1, since that refers to an evaluation of the specific function at t-1.
I won't write out all of the code, but I'll give you some of the basics:
When t = 0, return 2. This is your base case.
When t is between 0 and 6 inclusive or greater than 12, return an evaluation of the function at t-1 and add 2.
When t is between 7 and 12 both inclusive, return an evaluation of the function at t-1 and add log2(t).
Here's something to get you at least started in the right direction.
public double evaluateDistance(int t) {
if(t == 0) {
return 2;
} else if(t > 0 && t <= 6) || (t > 12) {
// Think about this - it would involve another call to evaluateDistance, but what is t again?
} else if(t >= 7 && t <= 12) {
// Another evaluation involving the function.
// For free, the change of base operation you'll need to get base-2 evaluation for the log:
return ??? + Math.log(t)/Math.log(2);
}
}

Think I figured it out. Sorry if I wasn't clear on what I needed, just needed to figure out how to write the equations in the function. Think I figured it out though.
public double move()
{
int t = 0;
if(t == 0) // After the first second, robot moves 2
{
distance = 2;
}
else if(t > 0 && t <= 6 || t > 12) // From seconds 0 to 6 and after 12, robot moves distance equation
{
distance = (2*t)+2;
}
else if(t >= 7 && t <= 12) // From seconds 7 to 12, robot moves distances equation
{
distance = (2*t)+(Math.log(t)/Math.log(2));
}
position = position + distance;
return position;
}
}

Supposed variable cannot be resolved as variable?

I'm doing a basic Java tutorial and below is the question.
Write a method that prints the numbers from 1 to 100. But for multiples of three print ÒFizzÓ instead of the number,and for the multiples of five print ÒBuzzÓ. For numbers which are multiples of both three and five print ÒFizzBuzzÓ."
My code is below
public static void fizzBuzz(){
for(int i = 0; i < 101; i= i +1 )
System.out.println(i);
if (i%3 == 0){
System.out.println("ÒFizzÓ");
}else if (i % 5 == 0){
System.out.println("ÒBuzzÓ");
}else if (i % 15 == 0){
System.out.println("ÒFizzBuzzÓ");
}
}
Eclipse tells me that "i" cannot be resolved as a variable. This is confusing to me as I thought I already defined "i" as an integer in my for loop? Thanks for taking the time to solve this newbie question :)

Add braces or your loop body ends after the first statement. Also, for your approach you need to test 15 first because it's a multiple of 3 and 5
for(int i = 0; i < 101; i++) { // <-- i++ is short for i = i + 1
System.out.println(i);
if (i % 15 == 0) {
System.out.println("ÒFizzBuzzÓ");
} else if (i % 5 == 0) {
System.out.println("ÒBuzzÓ");
} else if (i % 3 == 0) {
System.out.println("ÒFizzÓ");
}
}

I know a funny story about Apple who lost a few million dollars because a developer updated a code with an if block but... the if statement had only one instruction and no curly brackets and he did not see it. Thus, the code he was willing to add when the condition was met were actually ALWAYS executed.
In your case, you won't lose money but you surely did the same mistake :
for(int i = 0; i < 101; i= i +1 ) {
System.out.println(i);
if (i % 15 == 0){
System.out.println("ÒFizzBuzzÓ");
} else if (i%3 == 0){
System.out.println("ÒFizzÓ");
} else if (i % 5 == 0){
System.out.println("ÒBuzzÓ");
}
}

When Java says something cannot be resolved as a variable, it is usually been used outside the scope it was declared or it was not declared at all.In your case, your braceless for-loop is causing the problem.

Solving elimination using nested loops in java?

I was trying to solve a program challenge that solves this prompt
"When 2, 3, 4, 5, 6 eggs are removed at a time from a basket of eggs, the remaining amounts are 1, 2, 3, 4,5 eggs respectively. When 7 eggs are removed at a time, no eggs remain. What is the least number of eggs I could have had in the basket?"
I tried to make a program using nested loops and I feel like it should work, but when I run the program, it just prints blank space. I never get a number to satisfy the equation. Can someone help me, or show me what I did wrong please?
I'm only allowed to use nested loops and decision statements.
public class Program{
public static void main (String []args){
int c,d,e,f,g,h;
for (int j=1; j<1000; j++){
for (c=j; c>=1; c=c-2){
}
if (c==1){
for (d=j; d>=2; d=d-3){
}
if (d==2){
for (e=j; e>=3; e=e-4){
}
if (e==3){
for (f=j; f>=4; f=f-5){
}
if (f==4){
for (g=j; g>=5; g=g-6){
}
if (g==5){
for (h=j; g>=0; h=h-7){
}
if (h==0){
System.out.println(+j);
}
}
}
}
}
}
}
}
}

Try this:
public static void main(String[] args) {
int x = 7;
int result = -1;
while (true) {
if ((x % 2 == 1) && (x % 3 == 2) && (x % 4 == 3) && (x % 5 == 4)
&& (x % 6 == 5)) {
result = x;
break;
}
x += 7; // This because you know its multiple of 7
}
System.out.println("Result is: " + result);
}

int numberOfEggs = 0;
for (;;)
{
if (numberOfEggs % 2 == 1 &&
numberOfEggs % 3 == 2 &&
numberOfEggs % 4 == 3 &&
numberOfEggs % 5 == 4 &&
numberOfEggs % 6 == 5 )
return numberOfEggs;
else
numberOfEggs += 7;
}