Develop Reference

Can I, within the same file, use a previously printed line as an input to a new section?

public class Bonus1{
public static void main(String[] args) {
int n = Integer.parseInt(args[0]);
int[] numbers = new int[n];
for (int i = 0; i < n; i++ ) {
numbers[i] = i;
}
for (int i = 0; i < n; i++ ) {
int r = i + (int)(Math.random() * (n - i));
int tmp = numbers[i];
numbers[i] = numbers[r];
numbers[r] = tmp;
System.out.print(numbers[i]);
}
int min = Integer.MAX_VALUE;
int count = 0;
while(data.hasNext()){
int y = data.nextInt();
if(y < min){
min = y;
count += 1;
}
}
System.out.println(count);
}
}
this code isn't complete, the first 2 for-loops will generate an array between 0 to a given number in the commandline -1
So for example java Bonus1 10 would first generate an array between 0-9 and then it will shuffle these numbers around so that it creates a random permutation.
the while loop is something I've used before to read input and determine how many times a new lowest number is detected. so for example if I get the permutation 7 8 2 3 4 5 1 0 6 9 it will count 7 as the lowest, then 2 as the lowest and then 1 as the lowest and finally 0 as the lowest, making the total amount of times a new lowest number has been detected 4.
but this only works if I use inputs, I need to use the previously generated output as the input in the same file, is there a clever way to do that?

You should iterate for the array numbers like this.
public static void main(String[] args) {
int n = Integer.parseInt(args[0]);
int[] numbers = new int[n];
for (int i = 0; i < n; i++) {
numbers[i] = i;
}
for (int i = 0; i < n; i++) {
int r = i + (int) (Math.random() * (n - i));
int tmp = numbers[i];
numbers[i] = numbers[r];
numbers[r] = tmp;
System.out.print(numbers[i]);
}
System.out.println();
int min = Integer.MAX_VALUE;
int count = 0;
for (int i = 0; i < n; ++i) {
int y = numbers[i];
if (y < min) {
min = y;
++count;
}
}
System.out.println(count);
}
output:
6457098123
3

How to swap the largest number with the last number in an array?

I'm trying to create a program that asks the user to input a number which is how many random numbers between 1-100 will be generated in an array. Then I want the largest number to be swapped with the last number and the smallest number to be swapped with the first number. Here is my code so far:
import java.util.Scanner;
import java.util.Random;
public class smallbig
{
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
Random randomGenerator = new Random();
int num = scan.nextInt();
int[] myArray = new int[num];
for (int i = 0; i < myArray.length; ++i) {
int randomInt = randomGenerator.nextInt(100);
myArray[i] = randomInt;
}
int smallest = myArray[0];
int largest = myArray[0];
for (int i = 1; i < myArray.length; i++) {
if (myArray[i] > largest) {
largest = myArray[i];
}
if (myArray[i] < smallest) {
smallest = myArray[i];
}
}
for (int j = 1; j < myArray.length; j++) {
int first = myArray[0];
myArray[0] = smallest;
smallest = first;
int temp = largest;
int last = myArray.length;
myArray[last - 1] = largest;
temp = myArray[last - 1];
System.out.print(myArray[j] + " ");
}
}
}
I can't seem to get the numbers to properly swap. I created a loop which determines the smallest and largest numbers from the ones generated and these are stored. Then I create a loop which performs the necessary swaps but I can't seem to get it to work properly. It works fine for swapping the largest number with the last number but most of the time(not always) the outputted last number is also present somewhere else in the array. Here is what I mean:
input: 10
output: 62 48 34 0 91 14 64 60 91
I know there is a swapper method that I could use but I want to do it by manually swapping the numbers. Any help is appreciated, thanks.

you have one simple mistake, your loop should start from '0' when you perform the swap
for (int j = 0; j < myArray.length; j++) {
int first = myArray[0];
myArray[0] = smallest;
smallest = first;
int temp = largest;
int last = myArray.length;
myArray[last - 1] = largest;
temp = myArray[last - 1];
System.out.print(myArray[j] + " ");

Instead of a loop do
//find and stores poition of small
int smallPos = myArray.indexOf(small);
//stores tge values at 0
int tempSmall = myArray[0];
//swaps the values
myArray[0] = small;
myArray[smallPos] = smallTemp;
Just repeat this with the largest value and print it using a for loop. Tell me if it works.

I just tried this. Hope this helps.
public class App {
static int[] a = new int[100];
public static void main(String[] args) {
int i;
for(i = 0; i<a.length;i++)
a[i] = (int)(java.lang.Math.random() * 100);
int smallest = 0, largest = 0;
for(i =1; i<a.length; i++){
if(a[i] < a[smallest])
smallest = i;
if(a[i] > a[largest])
largest = i;
}
swap(0,smallest);
swap(a.length-1,largest);
for(i =0; i<a.length;i++)
System.out.print(a[i] + " ");
}
public static void swap(int i, int j){
int temp = a[i];
a[i] = a[j];
a[j] = temp;
}
}

Your last loop doesn't do anything loopy. It just does the same thing over and over. And what it does is not correct. It is swapping the smallest into the first element but it's not moving the first element anywhere: it's gone.
You need to keep track of where the largest and smallest elements were. Your swap logic doesn't take that into consideration.

Write this code
import java.util.Scanner;
import java.util.Random;
public class smallbig
{
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
Random randomGenerator = new Random();
int num = scan.nextInt();
int[] myArray = new int[num];
for (int i = 0; i < myArray.length; ++i) {
int randomInt = randomGenerator.nextInt(100);
myArray[i] = randomInt;
}
int smallest = myArray[0];
int largest = myArray[0];
int pos1,pos2;
for (int i = 1; i < myArray.length; i++) {
if (myArray[i] > largest) {
largest = myArray[i];
pos1=i;
}
if (myArray[i] < smallest) {
smallest = myArray[i];
pos2=i;
}
}
myArray[pos1]=myArray[myArray.length-1];
myArray[myArray.length-1]=largest;
myArray[pos2]=myArray[0];
myArray[0]=smallest;
for (int j = 1; j < myArray.length; j++) {
System.out.print(myArray[j] + " ");
}
}
}

i would advise against using a scanner or random values for testing since the result cannot be reproduced (at least not in an easy way). Be careful with what is an arrays index and what is the value at a specific index. This can lead to confusion very quickly. ^^
import java.util.Scanner;
import java.util.Random;
public class smallbig
{
private static int[] myArray;
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
Random randomGenerator = new Random();
//int num = scan.nextInt(); //skip this for testing ^^-d
int num = 10;
myArray = new int[num];
for (int i = myArray.length-1; i > 0; i--) {
//int randomInt = randomGenerator.nextInt(100);
int randomInt = i; //use test condition that can be reproduced!
myArray[i] = myArray.length-i;
}
int smallest = 0;
int largest = 0;
int smallestIndex = 0;
int largestIndex = 0;
for (int i = 0; i < myArray.length; i++) {
if (myArray[i] > largest) {
largest = myArray[i];
largestIndex = i;
}
if (myArray[i] < smallest) {
smallest = myArray[i];
smallestIndex = i;
}
}
switchIndexOfmyArray(0, smallestIndex);
switchIndexOfmyArray(myArray.length-1, largestIndex);
for (int j = 0; j < myArray.length; j++) {
System.out.print(myArray[j] + " ");
}
}
public static void switchIndexOfmyArray(int index, int switchWithIndex){
int temp = myArray[index];
myArray[index] = myArray[switchWithIndex];
myArray[switchWithIndex] = temp;
}
}
Yielding
0 1 8 7 6 5 4 3 2 9
I admit i was slow on this one since i am hungry and tired xD
Happy coding! ^^

You did well by finding smallest and largest. Issue was in swap. I refactor the swap method. May be it works.
import java.util.Scanner;
import java.util.Random;
public class smallbig
{
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
Random randomGenerator = new Random();
int num = scan.nextInt();
int[] myArray = new int[num];
for (int i = 0; i < myArray.length; ++i) {
int randomInt = randomGenerator.nextInt(100);
myArray[i] = randomInt;
}
for(int k=0; k < myArray.length; k++)
{
System.out.print(myArray[k] + " ");
}
System.out.println();
int smallest = myArray[0];
int largest = myArray[0];
int sIndx = 0;
int lIndx = 0;
for (int i = 1; i < myArray.length; i++) {
if (myArray[i] > largest) {
largest = myArray[i];
lIndx = i;
}
if (myArray[i] < smallest) {
smallest = myArray[i];
sIndx = i;
}
}
System.out.println();
System.out.println("Smallest = "+smallest);
System.out.println("largest = "+largest);
System.out.println("Smallest Index = "+sIndx);
System.out.println("largest Index = "+lIndx);
swapSmallAndLargest(num, myArray, sIndx, lIndx);
for(int k=0; k < myArray.length; k++)
{
System.out.print(myArray[k] + " ");
}
}
private static void swapSmallAndLargest(int num, int[] myArray, int sIndx, int lIndx) {
int temp = 0;
temp = myArray[sIndx];
myArray[sIndx] = myArray[0];
myArray[0] = temp;
temp = myArray[lIndx];
myArray[lIndx] = myArray[num-1];
myArray[num-1] = temp;
}
}

Out of Bounds Error in 2D Array with Dice Program

So I am creating a program that rolls z die x times with y sides, and I keep getting an out of bounds error at the first line in the first for loop. However I'm not sure why this is, the loop counts from 0 to (z-1). I'm basically in the home stretch of this program and I need the help of the stackoverflow community.
public class Ass11f {
public static void main(String[] args) {
EasyReader console = new EasyReader();
System.out.print("Enter how many times you want to roll the die: ");
int x = console.readInt();
System.out.print("Enter the amount of sides: ");
int y = console.readInt();
System.out.print("Enter the amount of die: ");
int z = console.readInt();
int[][] dice = new int[x][z];
int row = 0;
for (int i = 0; i<z; ++i){
dice[row][i] += ((int)(Math.random()*y)+1);
if ((i == z-1)&&(row!=x)) {
i = 0;
++row;
}
}
row = 0;
int[] sum = new int[x];
for (int j = 0; j<z; ++j){
sum[row]+=dice[j][row];
if ((j == z-1)&&(row!=x)) {
j = 0;
++row;
}
}
int[] counter = new int[2*y];
int k = 0;
while (k<sum.length){
for (int l = 0;l<((2*y)-1);++l){
if (sum[k]==l) ++counter[l];
if (l==((2*y)-1)) {
++k;
}
}
}
for (int m = 0;m<sum.length;++m) System.out.println(sum[m]+"'s: "+counter[m]+"times, "+((((double)counter[m])/x)*100)+"%");
}
}

first loop:
for (int i = 0; i<z; i++){
dice[row][i] += ((int)(Math.random()*y)+1);
if ((i == z-1)&&(row!=x-1)) {
i = -1;
++row;
}
}
second loop:
for (int j = 0; j<z; j++){
sum[row]+=dice[j][row];
if ((j == z-1)&&(row!=x-1)) {
j = -1;
++row;
}
}
Third loop: runs forever. I'm not sure what this is trying to achieve, so I can't fix it for you...

There are x rows but you are using z as the row loop
int[][] dice = new int[x][z]; <-- x is the row count
int row = 0;
for (int i = 0; i < z; ++i){ <--- The outer loop is iterating the rows (x),
Here's how to iterate through a 2D array
int[][] dice = new int[x][z];
for (int i = 0; i < x; i++){
for (int j = 0; j < z; j++){
// do something with dice[i][j]
}
}

Storing data in Arrays (Java)

I'm just a beginner in Java. Can someone please tell me how to arrange this program. In this program I want to store 10 marks in an array, and then output the ones that are equal to or greater than the average. Help would be appreciated.
public class ClassAverage{
public static void main (String Args []){
int sum = 0;
int mark[] = new int [10];
for(int c = 0; c < 10; c++){
System.out.print("Enter a mark: ");
mark[c] = Keyboard.readInt();
}
sum = sum + mark[c];
int average = sum / 10;
if(mark[c]>=average){
System.out.print(mark[c]);
}
}
}

You need loop the array twice. The first iteration sums all the elements and computes the average. And the other iteration outputs the elements that meet your constraints.
The code is below:
public class ClassAverage{
public static void main (String Args []){
int sum = 0;
int mark[] = new int [10];
// The first iteration sums all elements
for(int c = 0; c < 10; c++){
System.out.print("Enter a mark: ");
mark[c] = Keyboard.readInt();
sum = sum + mark[c];
}
int average = sum / 10;
// This iteration outputs elements that meet your requirements.
for(int c = 0; c < 10; c++){
if(mark[c]>=average){
System.out.print(mark[c]);
}
}
}
}

You need to add another for loop to iterate your array after calculating the average. Here is the updated code with the required for loop:
public static void main (String Args []){
int sum = 0;
int mark[] = new int [10];
for(int c = 0; c < 10; c++) {
System.out.print("Enter a mark: ");
mark[c] = Keyboard.readInt();
sum = sum + mark[c];
}
int average = sum / 10;
for(int c = 0; c < 10; c++) {
if(mark[c]>=average){
System.out.print(mark[c]);
}
}
}

public class aver{
public static void main (String Args []){
int sum = 0;
int mark[] = new int [10];
int average;
for(int c = 0; c < 10; c++){
System.out.print("Enter a mark: ");
mark[c] = Keyboard.readInt();
}
for(int c = 0; c < 10; c++){
sum = sum + mark[c];
}
average = sum / 10;
for(int c = 0; c < 10; c++){
if(mark[c]>=average){
System.out.println(mark[c]);
}
}
}
}

sum = sum + mark[c];
statement must be inside your loop.
public class ClassAverage{
public static void main (String Args []){
int sum = 0;
int mark[] = new int [10];
for(int c = 0; c < 10; c++)
{
System.out.print("Enter a mark: ");
mark[c] = Keyboard.readInt();
sum = sum + mark[c];
}
int average = sum / 10;
for(int c = 0; c < 10; c++)
{
if(mark[c]>=average)
{
System.out.print(mark[c]);
}
}
}

Just some modification in your code.
public class ClassAverage{
public static void main (String Args []){
int sum = 0;
int mark[] = new int [10];
for(int c = 0; c < 10; c++){
System.out.print("Enter a mark: ");
mark[c] = Keyboard.readInt();
sum = sum + mark[c];
}
int average = sum / 10;
for(int c = 0; c < 10; c++){
if(mark[c]>=average)
System.out.print(mark[c]);
}
}
Explanation
You need to add each element to sum to get the total. So add each element within the for loop after taking input
you also need to check each element to compare with the average. So you need to iterate the array again to compare each element.

Java permutations 2

I asked a question on helping me with this question about a week ago
Java permutations
, with a problem in the print permutation method. I have tidied up my code and have a working example that now works although if 5 is in the 5th position in the array it doesn't print it. Any help would be really appreciated.
package permutation;
public class Permutation {
static int DEFAULT = 100;
public static void main(String[] args) {
int n = DEFAULT;
if (args.length > 0)
n = Integer.parseInt(args[0]);
int[] OA = new int[n];
for (int i = 0; i < n; i++)
OA[i] = i + 1;
System.out.println("The original array is:");
for (int i = 0; i < OA.length; i++)
System.out.print(OA[i] + " ");
System.out.println();
System.out.println("A permutation of the original array is:");
OA = generateRandomPermutation(n);
printArray(OA);
printPermutation(OA);
}
static int[] generateRandomPermutation(int n)// (a)
{
int[] A = new int[n];
for (int i = 0; i < n; i++)
A[i] = i + 1;
for (int i = 0; i < n; i++) {
int r = (int) (Math.random() * (n));
int swap = A[r];
A[r] = A[i];
A[i] = swap;
}
return A;
}
static void printArray(int A[]) {
for (int i = 0; i < A.length; i++)
System.out.print(A[i] + " ");
System.out.println();
}
static void printPermutation(int[] p)
{
int n = p.length-1;
int j = 0;
int m;
int f = 0;
System.out.print("(");
while (f < n) {
m = p[j];
if (m == 0) {
do
f++;
while (p[f] == 0 && f < n);
j = f;
if (f != n)
System.out.print(")(");
}
else {
System.out.print(" " + m);
p[j] = 0;
j = m - 1;
}
}
System.out.print(" )");
}
}

I'm not too crazy about
int n = p.length-1;
followed by
while (f < n) {
So if p is 5 units long, and f starts at 0, then the loop will be from 0 to 3. That would seem to exclude the last element in the array.

You can use the shuffle method of the Collections class
Integer[] arr = new Integer[] { 1, 2, 3, 4, 5 };
List<Integer> arrList = Arrays.asList(arr);
Collections.shuffle(arrList);
System.out.println(arrList);

I don't think swapping each element with a random other element will give a uniform distribution of permutations. Better to select uniformly from the remaining values:
Random rand = new Random();
ArrayList<Integer> remainingValues = new ArrayList<Integer>(n);
for(int i = 0; i < n; i++)
remainingValues.add(i);
for(int i = 0; i < n; i++) {
int next = rand.nextInt(remainingValues.size());
result[i] = remainingValues.remove(next);
}
Note that if order of running-time is a concern, using an ArrayList in this capacity is n-squared time. There are data-structures which could handle this task in n log n time but they are very non-trivial.

This does not answer the problem you have identified.
Rather i think it identifies a mistake with your generateRandomPermutation(int n) proc.
If you add a print out of the random numbers generated (as i did below) and run the proc a few times it allows us to check if all the elements in the ARRAY TO BE permed are being randomly selected.
static int[] generateRandomPermutation(int n)
{
int[] A = new int[n];
for (int i = 0; i < n; i++)
A[i] = i + 1;
System.out.println("random nums generated are: ");
for (int i = 0; i < n; i++) {
int r = (int) (Math.random() * (n));
System.out.print(r + " ");
Run the proc several times.
Do you see what i see?
Jerry.