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Remix the String

I am stuck with this challenge, any help would be great.
'Create a function that takes both a string and an array of numbers as arguments. Rearrange the letters in the string to be in the order specified by the index numbers. Return the "remixed" string. Examples
remix("abcd", [0, 3, 1, 2]) ➞ "acdb"'
My attempt -
package edabitChallenges;
//Create a function that takes both a string and an array of numbers as arguments.
//Rearrange the letters in the string to be in the order specified by the index numbers.
//Return the "remixed" string.
public class RemixTheString {
public static String remix(String word, int[] array) {
char[] wordArray = word.toCharArray();
for (int i = 0; i < array.length; i++) {
char ch = ' ';
ch = wordArray[i];
wordArray[i] = wordArray[array[i]];
wordArray[array[i]] = ch;
}
String newString = new String(wordArray);
return newString;
}
public static void main(String[] args) {
System.out.println(remix("abcd", new int[] { 0, 3, 1, 2 }));
}
}

I would suggest just iterating the indices passed in the array[] input, and then building out the output string:
public static String remix(String word, int[] array) {
char[] wordArray = word.toCharArray();
StringBuilder output = new StringBuilder();
for (int i=0; i < array.length; i++) {
output.append(wordArray[array[i]]);
}
return output.toString();
}
public static void main(String[] args) {
System.out.println(remix("abcd", new int[] { 0, 3, 1, 2 })); // adbc
}
Here we use StringBuilder which exposes a handy append(char) method for adding one character at a time to the string in progress.

Java Algorithm regarding taking array of String and Integers to

I'm currently doing an activity that requires me to write this:
Write a definition for a static method stringHeads that inputs an array of ints p and a String s. For each of the ints n in p, the method builds the substring consisting of the first n characters in s (or the whole of s, if n is greater than the length of s). The method returns the array of these substrings.
My code is currently something like this:
public static String[] stringHeads(int[] p, String s) {
String[] rad = new String[p.length];
int e = 0;
for (int b : p)
e = b - 1
for (int de = 0; rad.length > de; de++)
rad[de] = s.substring(0,e);
for (String str : rad)
return str;
}
//Just ignore the rest
int[] a = {4, 2, 3, 2, 0 };
String b = "Radon"
stringHeads(a,b)
The output should be "Rado" , "Ra", "Rad", "Ra", "".
The error that I'm currently getting is that String cannot be converted to String[].
Basically my question is how to fix this error and if a better code can be written.

Three things:
e would be constant if you enter the second loop.
e could be larger than s.length() - you didn't handle this case.
You return a String instead of a String[]
And please always use braces if you use loops, even if the loop only contains one statement. It is much more readable and can avoid errors.
I think you will have to rethink your whole function. Don't know if it would be helpful to write the function for you.
Hints:
Write only one loop!
String[] rad = new String[p.length];
for (int i=0; i < p.length; i++) {
if (s.length() < ??) {
rad[i] = s.substring(0,??);
} else {
??
}
}
return rad;
I hope this will help you to get the answer yourself.

See my code below hope it helps:-
I provided the comments instead of explaining it in paragraph.
As for your error, you are returning String from method but expected is an array of String.
public static void main(String[] args){
int[] a = {4, 2, 3, 2, 0 };
String b = "Radon";
String[] output=stringHeads(a,b);
for(String s:output){
System.out.println(s);
}
}
Your method can be like below:
public static String[] stringHeads(int[] p, String s) {
String[] rad = new String[p.length];
int e = 0;
//Iterate over integer array
for(int index=0; index<p.length; index++){
//Extracting the integer value from array one by one
e=p[index];
//If integer value is greater than String length
if(e>s.length()){
//Put the entire String in String array
rad[index]=s;
}else{
//Put the Substring value with range 0 to e i.e. integer value
rad[index]=s.substring(0,e);
}
}
return rad;
}

You could simplify you code by just using a single iteration with an alternative variable.
public static void main (String[] args) throws java.lang.Exception
{
int[] a = {4, 2, 3, 2, 0 };
String b = "Radon";
String[] result = stringHeads(a,b);
for(String x : result) System.out.println(x);
//Or you can write a separate display method instead.
}
public static String[] stringHeads(int[] p, String s)
{
String[] rad = new String[p.length];
//Use this variable for array allocation/iteration.
int i=0;
//Simply iterate using this for-each loop.
// This takes care of array allocation/ substring creation.
for (int x : p)
rad[i++] = s.substring(0,x);
return rad;
}

Please check the code below
public static String[] stringHeads(int[] intArray, String str) {
String[] result = new String[intArray.length];
int count=0;
for (int intValue : intArray)
{
result[count] = str.substring(0,intValue);
count++;
}
return result;
} //Just ignore the rest
public static void main(String[] args) {
int[] a = {4, 2, 3, 2, 0 };
String b = "Radon";
String[] strArray=stringHeads(a,b);
int count=0;
for(String str:strArray)
System.out.println(++count+"" +str);
}

Change your method like this
public static String[] stringHeads(int[] p, String s) {
String[] rad = new String[p.length];
int e = 0;
for (int b : p) {
rad[e] = s.substring(0, b);
e++;
}
return rad;
}
For use this method
public static void main(String[] args) {
int[] a = {4, 2, 3, 2, 0};
String b = "Radon";
String[] stringHeads = stringHeads(a, b);
for (String stringHead : stringHeads) {
System.out.println(stringHead);
}
}
Output is
Rado
Ra
Rad
Ra

There is no need for the for loop that iterates through the integer array p
public static String[] stringHeads(int[] p, String s) {
String[] rad = new String[p.length];
for (int de = 0; de < p.length; de++){
if (p[de] < s.length())
rad[de] = s.substring(0,p[de]);
else
rad[de]=s;
}
return rad;
}

public static String[] stringHeads(int[] p, String s) {
String[] rad = new String[p.length];
int e = 0;
for (int b : p) {
if(b<=s.length()){
rad[e] = s.substring(0, b);
}
e++;
}
return rad;
}

Is there any method or idea that can select characters from a string at indices which are multiple of given 'n' to get the result string?

If I have this string
String str="characters";
the result would like following
result="caatr";
what I have done is selecting char by char from the given string until we get the result. The chars are selected at indices which are multiples of given n. Example: if n=2, the relevant indices to be selected are 0, 2, 4 ... and for n = 3, the indices are 0, 3, 6...
I have solved it in two ways and are almost the same but is there any other ways?
char[] arr = str.toCharArray();
String s="";
for(int i=0;i<str.length();i=i+n)
s=s+arr[i]+"";
the other one is
String result = "";
for (int i=0; i<str.length(); i = i + n)
result = result + str.charAt(i);

public static void main(String args[]) {
System.out.println(getResultOf("characters"));
}
private static String getResultOf(String input) {
boolean skip = false;
StringBuilder sb = new StringBuilder();
for (char ch : input.toCharArray()) {
if (!skip) {
sb.append(ch);
}
skip = !skip;
}
return sb.toString();
}

Sort ArrayList using predefined list of indices

I am trying to sort an ArrayList using a predefined array of indices.
My current example uses a copy of the original ArrayList for sorting and therefore is not scalable for ArrayLists of larger objects
package sortExample;
import java.awt.List;
import java.util.ArrayList;
import java.util.Arrays;
public class sortExample {
public static void main(String[] args) {
String [] str = new String[] {"a","b","c","d"};
ArrayList<String> arr1 = new ArrayList<String>(Arrays.asList(str));
int [] indices = {3,1,2,0};
ArrayList<String> arr2 = new ArrayList(arr1.size());
for (int i = 0; i < arr1.size(); i++) {
arr2.add("0");
}
int arrIndex = 0;
for (int i : indices){
String st = arr1.get(arrIndex);
arr2.set(i, st);
arrIndex++;
}
System.out.println(arr1.toString());
System.out.println(arr2.toString());
}
}

For reusing same data, please see my solution:
public static void main(String[] args) {
String[] strs = new String[]{"a", "b", "c", "d"};
int[] indices = {3, 1, 2, 0};
String tmp;
for (int i = 0; i < strs.length; i++) {
if (i != indices[i]) {
tmp = strs[i];
strs[i] = strs[indices[i]];
strs[indices[i]] = tmp;
indices[indices[i]] = indices[i];
indices[i] = i;
}
}
for (int i : indices) {
System.out.print(i + " ");
}
System.out.println();
for (String str : strs) {
System.out.print(str + " ");
}
}
Output is:
0 1 2 3
d b c a

Alternate reorder in place based on cycles. Note that indices will be changed to {0,1,2,3}. I don't have Java installed (yet), so I converted working C++ code to what I think is proper Java syntax.
for (int i = 0; i < arr1.size(); i++) {
if(i != indices[i]) {
String st = arr1.get(i);
int t = indices[i];
int k = i;
int j;
while(i != (j = indices[k])){
arr1.set(k, arr1.get(j));
indices[k] = k;
k = j;
}
arr1.set(k, st);
indices[k] = k;
}
}
For this specific case {3,1,2,0}, all this does is swap 0 and 3. The longest cycle occurs when the indices are rotated, such as {3 0 1 2}, in which case st=arr1[0], arr1[0] = arr1[3], arr[3] = arr1[2], arr1[2] = arr1[1], arr1[1] = st.

There is a (a little bit) more simple solution:
int [] indices = {3,1,2,0};
ArrayList<String> arr2 = new ArrayList<String>();
for (int i = 0; i < arr1.size(); i++) {
arr2.add(arr1.get(indices[i]));
}

At the below, just use "indices" for a new array.
public class Sorting {
public static void main(String[] args) {
String [] str = new String[] {"a","b","c","d"};
int [] indices = {3,1,2,0};
String sorted [] = new String [str.length] ;
int i = 0;
for (String string : str) {
sorted[indices[i]] = string;
i++;
}
for (String string : sorted) {
System.out.print(string + " ");
}
}
}
prints: d b c a

Extraction of numerals from a string

I need to extract the numerals in a given string and store them in a separate array such that each index stores a individual number in the string.
Ex-"15 foxes chases 12 rabbits". I need the numbers 15 and 12 to be stored in a[0] and a[1].
String question=jTextArea1.getText();
String lower=question.toLowerCase();
check(lower);
public void check(String low)
{
int j;
String[] ins={"into","add","Insert"};
String cc=low;
for(int i=0;i<2;i++)
{
String dd=ins[i];
if(cc.contains(dd))
{
j=1;
insert(cc);
break;
}
}}
public void insert(String low)
{
String character = low;
int l=low.length();
int j[]=new int[20];
int m=0;
for(int k=0;k<=2;k++)
{
j[k]=0;
for(int i=0;i<l;i++)
{
char c = character.charAt(i);
if (Character.isDigit(c))
{
String str=Character.toString(c);
j[k]=(j[k]*10)+Integer.parseInt(str);
m++;
}
else if (Character.isLetter(c))
{
if(m>2)
{
break;
}
}}}

Regex is the best option for you.
//Compilation of the regex
Pattern p = Pattern.compile("(\d*)");
// Creation of the search engine
Matcher m = p.matcher("15 foxes chases 12 rabbits");
// Lunching the searching
boolean b = m.matches();
// if any number was found then
if(b) {
// for each found number
for(int i=1; i <= m.groupCount(); i++) {
// Print out the found numbers;
// if you want you can store these number in another array
//since m.group is the one which has the found number(s)
System.out.println("Number " + i + " : " + m.group(i));
}
}
You must import java.util.regex.*;

Assuming you can't use a Collection like a List, I would start by splitting on white space, using a method to count the numbers in that array (with a Pattern on digits), and then build the output array. Something like
public static int getNumberCount(String[] arr) {
int count = 0;
for (String str : arr) {
if (str.matches("\\d+")) {
count++;
}
}
return count;
}
And then use it like
public static void main(String[] args) {
String example = "15 foxes chases 12 rabbits";
String[] arr = example.split("\\s+");
int count = getNumberCount(arr);
int[] a = new int[count];
int pos = 0;
for (String str : arr) {
if (str.matches("\\d+")) {
a[pos++] = Integer.parseInt(str);
}
}
System.out.println(Arrays.toString(a));
}
Output is (as requested)
[15, 12]

To extract numerals from Strings use the following code:
String text = "12 18 100";
String[] n = text.split(" ");
int[] num = n.length;
for (int i =0; i < num.length;i++) {
num[i] = Integer.parseInt(n[i]);
};
All the string numbers in the text will be then integers

I believie it should be
String str = "12 aa 15 155";
Scanner scanner = new Scanner( str );
while( scanner.hasNext() )
{
if( scanner.hasNextInt() )
{
int next = scanner.nextInt();
System.out.println( next );
}
else
{
scanner.next();
}
}
scanner.close();