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Reverse and sum the number occurrence in string - java

I would like to write a function that will be reverse a number and then sum it up.
For example, the input string is
We have 55 guests in room 38
So the expected output should be
83 + 55 = 138
I have face a question is that I can't read the last number
example:
input string is '8 people'
output is 0
Here's the code I've written :
int total = 0;
String num = "";
String a = input.nextLine();
for (int i = a.length() - 1; i > 0; i--) {
if (Character.isDigit(a.charAt(i))) {
num += a.charAt(i);
if (!Character.isDigit(a.charAt(i - 1))) {
total += Integer.valueOf(num);
num = "";
}
}
}

All you really need to do is :
String input = "We have 55 guests in room 38";
int sum = 0;
String[] split = input.split(" "); // split based on space
for (int i = 0; i < split.length; i++) {
if (split[i].matches("[0-9]+")) {
sum = sum + Integer.parseInt(new StringBuffer(split[i]).reverse().toString());
}
}
System.out.println(sum);
Explanation:
Here we use regex to check if the String split contains only
digits.
Now we reverse the String and then parse it to an int before
summing.

Try this and works for any input in the form "We have x guests in room y". For your program however, instead if the for loop > 0 do > -1 I think:
Scanner scan = new Scanner(System.in);
scan.next(); scan.next();
String numberOne = "" + scan.nextInt();
scan.next(); scan.next(); scan.next();
String numberTwo = "" + scan.nextInt();
// String numberOne = "" + scan.nextInt(), numberTwo = "" + scan.nextInt();
String numberOneReversed = "", numberTwoReversed = "";
for(int k = numberOne.length() - 1; k > -1; k--)
numberOneReversed += numberOne.charAt(k);
for(int k = numberTwo.length() - 1; k > -1; k--)
numberTwoReversed += numberTwo.charAt(k);
int sum = Integer.parseInt(numberOneReversed) + Integer.parseInt(numberTwoReversed);
System.out.println("" + numberOneReversed + " + " + numberTwoReversed + " = " + sum);
scan.close();
Note for your program as defined in your question:
for (int i = a.length() - 1; i > -1; i--) {
instead of
for (int i = a.length() - 1; i > 0; i--) {
and
if (i != 0 && !Character.isDigit(a.charAt(i - 1))) {
instead of
for (int i = a.length() - 1; i > 0; i--) {
Will return the sum correctly.

Okay here is what I created using BigIntegers instead of ints:
public static BigInteger nameOfFunctionGoesHere(String input) {
BigInteger total = new BigInteger(new byte[] {0});
int i = 0;
while (i < input.length()) {
if (Character.isDigit(input.charAt(i))) {
int j = i + 1;
while (!(j >= input.length()) && Character.isDigit(input.charAt(j))) {
j++;
}
String num = input.substring(i, j);
char[] flipped = new char[num.length()];
for (int n = num.length() - 1; n >= 0; n--) {
flipped[n] = num.charAt(num.length() - (n + 1));
}
total = total.add(new BigInteger(new String(flipped)));
i = j;
} else {
i++;
}
}
return total;
}
You can of course use ints as well like this:
public static int nameOfFunctionGoesHere(String input) {
int total = 0;
int i = 0;
while (i < input.length()) {
if (Character.isDigit(input.charAt(i))) {
int j = i + 1;
while (!(j >= input.length()) && Character.isDigit(input.charAt(j))) {
j++;
}
String num = input.substring(i, j);
char[] flipped = new char[num.length()];
for (int n = num.length() - 1; n >= 0; n--) {
flipped[n] = num.charAt(num.length() - (n + 1));
}
total = total + Integer.parseInt(new String(flipped));
i = j;
} else {
i++;
}
}
return total;
}
With longs too:
public static long nameOfFunctionGoesHere(String input) {
long total = 0;
int i = 0;
while (i < input.length()) {
if (Character.isDigit(input.charAt(i))) {
int j = i + 1;
while (!(j >= input.length()) && Character.isDigit(input.charAt(j))) {
j++;
}
String num = input.substring(i, j);
char[] flipped = new char[num.length()];
for (int n = num.length() - 1; n >= 0; n--) {
flipped[n] = num.charAt(num.length() - (n + 1));
}
total = total + Long.parseLong(new String(flipped));
i = j;
} else {
i++;
}
}
return total;
}

In Java Why can't I get 9 characters from decimal numbers over 255? Is it the sign bit?

This is for the headstails java homework assignment that you can find a few places online (like http://www.javaproblems.com/2013/01/medium-problem-tricky-heads-and-tails.html)
The idea is to input a decimal 0 to 511 and have it output a 3 x 3 matrix of H or T for 0 or 1's (mine works 0 to 255)
Here's my attempt though, that I couldn't get working:
public static void main(String[] args) {
#SuppressWarnings("resource")
Scanner keyboard = new Scanner(System.in);
//System.out.println("Please enter a number between 0 and 511: ");
//int num = keyboard.nextInt();
int num = 458;
String binNum = "";
int temp;
String[][] coinArr = new String[3][3]; // = [][];
while(num > 0)
{
temp = (int) (num % 2);
binNum = binNum + "" + temp;
num = (int) (num / 2);
}
System.out.println("binNum length is " + binNum.length());
System.out.println("binNum is " + binNum);
binNum = String.format((binNum.length() < 9 ? ("%0"+ (9 - binNum.length())+"d%s") : "%0$d%s"), 0 ,binNum);
System.out.println("binNum length is " + binNum.length());
System.out.println("binNum is " + binNum);
int k=0;
for(int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
binNum = binNum.replaceAll("0", "H");
binNum = binNum.replaceAll("1", "T");
coinArr[i][j] = binNum.substring(k, k+1);
k++;
System.out.print(coinArr[i][j]);
}
System.out.println();
}
}

Your conversion from decimal to binary is wrong, the correct one is :
while(num > 0)
{
temp = (int) (num % 2);
binNum = temp + "" + binNum;
num = (int) (num / 2);
}
Then you only need 9 characters in your binNum :
binNum = binNum.length() < 9 ? String.format("%0"+ (9 - binNum.length())+"d%s", 0 ,binNum) : binNum;
// You don't need this inside your loop
binNum = binNum.replaceAll("0", "H");
binNum = binNum.replaceAll("1", "T");
int k=0;
for(int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
coinArr[i][j] = String.valueOf(binNum.charAt(k));
k++;
System.out.print(coinArr[i][j]);
}
System.out.println();
}

There are 2 issues:-
1) Change
binNum = binNum + "" + temp;
to
binNum = temp + binNum;
2) Change
binNum = String.format((binNum.length() < 9 ? ("%0"+ (9 - binNum.length())+"d%s") : "%0$d%s"), 0 ,binNum);
to
binNum = String.format("%09d", Integer.parseInt(binNum));

How can I implement a sequence of numbers in this Prime number generator?

I'm unsure of how to create a sequence of numbers that can be placed before each iteration of printed prime numbers. Thank you for any help you can offer.
public class CountingPrimes {
public static void main(String[] args) {
int flag = 0, i, j;
Scanner sc = new Scanner(System.in);
System.out.println("Enter the 1st number: ");
int firstNum = sc.nextInt();
System.out.println("Enter the 2nd number: ");
int secondNum = sc.nextInt();
System.out.println("Counting prime numbers between "
+ firstNum + " and " + secondNum + ":");
for (i = firstNum; i <= secondNum; i++) {
for (j = 2; j < i; j++) {
if (i % j == 0) {
flag = 0;
break;
} else {
flag = 1;
}
}
if (flag == 1) {
System.out.println(i);
}
}
}
}
Right now, my code outputs (after the user enters their two numbers):
Counting prime numbers between 1 and 14:
3
5
7
11
13
What I need my code to look like:
Counting prime numbers between 1 and 14:
1. 3
2. 5
3. 7
4. 11
5. 13
Also, if you could see any errors or improvements I could change, I would greatly appreciate it. Thank you again!

You can use a counter and print the counter as you print the prime number. Increment the counter each time.
int counter = 1;
int flag = 0, i, j;
.....
if (flag == 1) {
System.out.format("%d. %d\n", counter, i);
counter++;
}

a simple change:
import java.util.Scanner;
public class CountingPrimes {
public static void main(String[] args) {
int flag = 0, i, j;
int count = 0;
Scanner sc = new Scanner(System.in);
System.out.println("Enter the 1st number: ");
int firstNum = sc.nextInt();
System.out.println("Enter the 2nd number: ");
int secondNum = sc.nextInt();
System.out.println("Counting prime numbers between "
+ firstNum + " and " + secondNum + ":");
for (i = firstNum; i <= secondNum; i++) {
for (j = 2; j < i; j++) {
if (i % j == 0) {
flag = 0;
break;
} else {
flag = 1;
}
}
if (flag == 1) {
System.out.println(++count + "." + i);
}
}
}
}

Just add a count variable and increment it whenever you output a number:
...
int count = 0;
for (i = firstNum; i <= secondNum; i++) {
...
if (flag == 1) {
count++;
System.out.format("%d. %d%n", count, i);
}
}

Declare Count before for loop
int count = 0;
and then increment the count on every prime number.
if (flag == 1) {
System.out.println(++count+". "+i);
}
}

How to convert an array to String format without commas/brackets and add parentheses as values

I want to take the array of random values I've generated and print the aforementioned array with parentheses outside the longest run of the same number.
For example, if the array was [0,1,1,1,2,4,7,4] I'd like to receive 0(111)2474 as an output.
This is my code thus far.
import java.util.Random;
import java.util.Arrays;
/**
* Write a description of class ArrayRunner1 here.
*
* #author Ibrahim Khan
* #version (a version number or a date)
*/
public class ArrayRunner1 {
/**
* This method will generate my random numbers for my array.
* #param min minimum random value wanted
* #param max maximum random value wanted
* #return randomNum a random number between 1 and 6 inclusive
*/
public static int randInt(int min, int max) {
Random rand = new Random();
int randomNum = rand.nextInt((max - min) + 1) + min;
return randomNum;
}
public static void main(String[] args) {
System.out.println("\f");
//Part 1 - Generate a random array of length 40 with random 1-6 inclusive
int[] array1 = new int[40];
for (int i = 0; i < array1.length; i++) {
array1[i] = randInt(1, 6);
}
System.out.println(Arrays.toString(array1));
//Counts and RETURN: reports how many times each number is present
int counter1 = 0;
int counter2 = 0;
int counter3 = 0;
int counter4 = 0;
int counter5 = 0;
int counter6 = 0;
for (int i = 0; i < array1.length; i++) {
if (array1[i] == 1) {
counter1++;
}
if (array1[i] == 2) {
counter2++;
}
if (array1[i] == 3) {
counter3++;
}
if (array1[i] == 4) {
counter4++;
}
if (array1[i] == 5) {
counter5++;
}
if (array1[i] == 6) {
counter6++;
}
}
System.out.println("There are " + counter1 + " ones.");
System.out.println("There are " + counter2 + " twos.");
System.out.println("There are " + counter3 + " threes.");
System.out.println("There are " + counter4 + " fours.");
System.out.println("There are " + counter5 + " fives.");
System.out.println("There are " + counter6 + " sixes.");
//Counts the longest run of the same number. A run continues only when consecutive numbers have the same value.
//RETURN: The repeated number and the length of the run is then printed
int counter = 1;
int runMax = 1;
int runMin = 0;
int variableNum = 0;
int startCounter = 0;
int endCounter = 0;
for (int i = 0; i < array1.length - 1; i++) {
if (array1[i] == array1[i + 1]) {
counter++;
if (counter >= runMax {
runMax = counter;
runMin = i - counter + 1;
variableNum = array1[i];
startCounter = i - counter + 2;
endCounter = i + counter - 1;
}
} else {
counter = 1;
}
}
System.out.println("The longest run is " + runMax + " times and the number is " + variableNum + ". ");
System.out.println("The run starts at " + startCounter + " and ends at " + endCounter);
//Prints the array with parentheses outside the longest run, if there is more than one max run, use the last one.
}
}

try this code:
import java.util.Arrays;
import java.util.Random;
public class Snippet {
/**
* This method will generate my random numbers for my array.
*
* #param min
* minimum random value wanted
* #param max
* maximum random value wanted
* #return randomNum a random number between 1 and 6 inclusive
*/
public static int randInt(int min, int max) {
Random rand = new Random();
int randomNum = rand.nextInt((max - min) + 1) + min;
return randomNum;
}
public static void main(String[] args) {
System.out.println("\f");
// Part 1 - Generate a random array of length 40 with random 1-6
// inclusive
int[] array1 = new int[40];
for (int i = 0; i < array1.length; i++) {
array1[i] = randInt(1, 6);
}
System.out.println(Arrays.toString(array1));
// Counts and RETURN: reports how many times each number is present
int counter1 = 0;
int counter2 = 0;
int counter3 = 0;
int counter4 = 0;
int counter5 = 0;
int counter6 = 0;
for (int i = 0; i < array1.length; i++) {
if (array1[i] == 1) {
counter1++;
}
if (array1[i] == 2) {
counter2++;
}
if (array1[i] == 3) {
counter3++;
}
if (array1[i] == 4) {
counter4++;
}
if (array1[i] == 5) {
counter5++;
}
if (array1[i] == 6) {
counter6++;
}
}
System.out.println("There are " + counter1 + " ones.");
System.out.println("There are " + counter2 + " twos.");
System.out.println("There are " + counter3 + " threes.");
System.out.println("There are " + counter4 + " fours.");
System.out.println("There are " + counter5 + " fives.");
System.out.println("There are " + counter6 + " sixes.");
// Counts the longest run of the same number. A run continues only when
// consecutive numbers have the same value.
// RETURN: The repeated number and the length of the run is then printed
int counter = 1;
int runMax = 0;
int runMin = 0;
int variableNum = 0;
int startCounter = 0;
int endCounter = 0;
for (int i = 0; i < array1.length - 1; i++) {
if (array1[i] == array1[i + 1]) {
counter++;
if (counter >= runMax) {
runMax = counter;
startCounter = i - counter +2;
// runMin = i-counter+1;
variableNum = array1[i];
endCounter = i+1;
}
} else {
counter = 1;
}
}
System.out.println("The longest run is " + runMax
+ " times and the number is " + variableNum + ". ");
System.out.println("The run starts at " + startCounter
+ " and ends at " + endCounter);
for (int i = 0; i < array1.length; i++) {
if (i==startCounter) {
System.out.print("(");
}
System.out.print(array1[i]);
if (i==endCounter) {
System.out.print(")");
}
}
System.out.println();
// Prints the array with parentheses outside the longest run, if there
// is more than one max run, use the last one.
}
}

Okay. I think I have this. The first answer was close, but if you run the program a few times, you discover issues. There is a logic error somewhere in your above code, but I have a work around. I think it is how you get the endCounter. It seems to count odd. But I got the program to work as far as I can tell. Try this out. I have run it several times and it seems consistent.
import java.util.Random;
import java.util.Arrays;
/**
* Write a description of class ArrayRunner1 here.
*
* #author Ibrahim Khan
* #version (a version number or a date)
*/
public class ArrayRunner1 {
/**
* This method will generate my random numbers for my array.
* #param min minimum random value wanted
* #param max maximum random value wanted
* #return randomNum a random number between 1 and 6 inclusive
*/
public static int randInt(int min, int max) {
Random rand = new Random();
int randomNum = rand.nextInt((max - min) + 1) + min;
return randomNum;
}
public static void main(String[] args) {
System.out.println("\f");
//Part 1 - Generate a random array of length 40 with random 1-6 inclusive
int[] array1 = new int[40];
for (int i = 0; i < array1.length; i++) {
array1[i] = randInt(1, 6);
}
System.out.println(Arrays.toString(array1));
//Counts and RETURN: reports how many times each number is present
int counter1 = 0;
int counter2 = 0;
int counter3 = 0;
int counter4 = 0;
int counter5 = 0;
int counter6 = 0;
for (int i = 0; i < array1.length; i++) {
if (array1[i] == 1) {
counter1++;
}
if (array1[i] == 2) {
counter2++;
}
if (array1[i] == 3) {
counter3++;
}
if (array1[i] == 4) {
counter4++;
}
if (array1[i] == 5) {
counter5++;
}
if (array1[i] == 6) {
counter6++;
}
}
System.out.println("There are " + counter1 + " ones.");
System.out.println("There are " + counter2 + " twos.");
System.out.println("There are " + counter3 + " threes.");
System.out.println("There are " + counter4 + " fours.");
System.out.println("There are " + counter5 + " fives.");
System.out.println("There are " + counter6 + " sixes.");
//Counts the longest run of the same number. A run continues only when consecutive numbers have the same value.
//RETURN: The repeated number and the length of the run is then printed
int counter = 1;
int runMax = 1;
int runMin = 0;
int variableNum = 0;
int startCounter = 0;
int endCounter = 0;
for (int i = 0; i < array1.length - 1; i++) {
if (array1[i] == array1[i + 1]) {
counter++;
if (counter >= runMax ){
runMax = counter;
runMin = i - counter ;// was plus one I cahnged this.
variableNum = array1[i];
startCounter = i - counter + 2;
endCounter = i + counter -1;
}
} else {
counter = 1;
}
}
System.out.println("The longest run is " + runMax + " times and the number is " + variableNum + ". ");
System.out.println("The run starts at " + startCounter + " and ends at " + endCounter);
//Prints the array with parentheses outside the longest run, if there is more than one max run, use the last one.
String output = "";// added this
for(int x = 0; x < array1.length; x++)
{
if( x == startCounter)
{
output += "("+array1[x];
}
else if( x == startCounter + runMax )
{
else if( x == startCounter + runMax )
{
if(x == array1.length-1)
{
output += ")";
}
else
{
output += ")"+array1[x];
}
}
else
{
output += array1[x];
}
}
System.out.print("\n"+output);
}
}

Here's a shorter, more generic solution. This method takes any array of ints and prints parenthesis around the longest run of numbers. If there are two runs of the same lengths it prints it around the first one.
public String makeString(int[] ints) {
if (ints.length == 0) return ""; // Quit early if there's nothing to do.
// Initialize variables.
int lastNumber = ints[0];
// We keep track of the all time best run. Defaults to first int found.
int bestStart = 0;
int bestRun = 1;
// ... as well as the current run.
int currentStart = 0;
int currentRun = 1;
String s = ""+ints[0];
// Starting from the second int, we check if the current run is continuing.
for (int i = 1; i < ints.length; i++) {
int current = ints[i];
// If the current run continues, we update currentStart/currentRun, else we reset it.
if (current == lastNumber) {
currentRun++;
} else {
currentStart = i;
currentRun = 1;
}
// Now we check if the currentRun is better than the best.
// If so, we update bestStart/bestRun.
if (currentRun > bestRun) {
bestStart = currentStart;
bestRun = currentRun;
}
lastNumber = current;
s += current;
}
// Now that we've found it, we insert parenthesis aaaaaaand we're done!
return s.substring(0, bestStart)
+"("+s.substring(bestStart, bestStart+bestRun)+")"
+s.substring(bestStart+bestRun);
}

String index out of range (Repeating Sequence of digits)

I seem to be having a problem with my code which is to look for the repeating sequence of digits. I have converted(?) double to string because I get the error unreachable statement. (which I guess helps to looking for the reason why I get the error I have now?).
Whenever I run it, it goes fine until I finish entering N and D.
It'll say "Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 3"
Here is my code below:
import java.util.*;
public class RepeatingSequence{
public static void main(String[] args){
Scanner in = new Scanner(System.in);
System.out.print("Enter N,D: ");
int numerator = in.nextInt();
int denominator = in.nextInt();
double quotient = numerator / denominator;
String number = "" + quotient;
char n = number.charAt(0);
int j = 1;
int z = 0;
String output = "";
char[] index = number.toCharArray();
for ( int i = 2; number.charAt(j) != number.charAt(i); i++ ){
index[z] = number.charAt(z);
index[j] = number.charAt(j);
index[i] = number.charAt(i);
output = output + index[i];
if ( index[i] != index[z] ){
System.out.print(index[z] + ".(" + index[j] + output + ")");
}
}
}
}

just add i < number.length() to the condition
( int i = 2; i < number.length() && number.charAt(j) != number.charAt(i); i++ )

For your exception, I think you should write safer code - something on the lines of:
int len = number.length();
for ( int i = 2; (i < len) && (j < len) &&
number.charAt(j) != number.charAt(i); i++ ){
...
}
I am not attempting to solve the problem that you are trying to solve but just the problem you are facing. Sorry for that.

I changed your code a little bit try it out and see what you think:
public static void main(String[] args){
Scanner in = new Scanner(System.in);
System.out.print("Enter N,D: ");
double numerator = in.nextDouble();
double denominator = in.nextDouble();
double quotient = numerator / denominator;
String number = "" + quotient;
char n = number.charAt(0);
int j = 1;
int z = 0;
String output = "";
char[] index = number.toCharArray();
int max = -1;
int currentNumber = -1;
int temp = -1;
int tempMax = -1;
System.out.println("" + quotient);
boolean check = true;
for(int i = (number.indexOf(".") + 1); i < index.length; i++)
{
if(max == -1)
{
currentNumber = i;
temp = i;
max = 1;
tempMax = 1;
}
else
{
if(index[i] == index[i-1])
{
tempMax++;
}
else
{
if(tempMax > max)
{
check = false;
max = tempMax;
currentNumber = temp;
}
tempMax = 1;
temp = i;
}
}
}
if(check)
{
max = tempMax;
}
System.out.println(index[currentNumber] + " repeats " + max + " times.");
}
Example of input/output:
Enter N,D: 1
3
0.3333333333333333
3 repeats 16 times.