import java.lang.Math;
public class radixSort{
public static int getFreeSpace(Integer array[]){ //this function gets the first occurence of a null element in the array
int i;
for (i = 0; i < array.length;i++){
if (array[i] == null){
break;
}
}
return i;
}
public static Integer[] flatten(Integer array[][]){ //this function flattens the multi-dimensional lsdArray to a single dimension array
Integer finalArray[] = new Integer[1000];
for (int i = 0; i < array.length; i++){
Integer[] currentArray = array[i];
for (int j = 0; j < currentArray.length; j++){
if (array[i][j] != null){
int index = getFreeSpace(finalArray);
finalArray[index] = currentArray[j];
}
else;
}
}
return finalArray;
}
public static Integer getMaxDigits(Integer array[]){ //this function gets the largest number of digits in the array. this is helplful for getting the number of times the array is passed into the sort
Integer max = 0;
Integer m = 0;
for (int i = 0; i < array.length; i++){
m = Math.max(max, array[i]);
}
String s = m.toString();
return s.length();
}
public static Integer[] radixSortFunc(Integer array[],Integer maxDigits, Integer counter){ //the sorting algorithm
Integer[][] lsdArray = new Integer[10][15];
if (counter <= maxDigits){
for (Integer i = 0; i < array.length; i++){
double temp = Math.pow(10,counter+1);
int powOfTen = (int) temp;
int term = (array[i] % powOfTen );
temp = Math.pow(10,counter);
powOfTen = (int) temp;
int digit = Math.floorDiv(term,powOfTen);
Integer[] currentArray = lsdArray[digit];
Integer index = getFreeSpace(currentArray);
currentArray[index] = array[i];
lsdArray[digit] = currentArray;
}
counter++;
return radixSortFunc(flatten(lsdArray),maxDigits,counter);
}
else{
return array;
}
}
public static void main(String[] args){
Integer[] array ={12,23,45,23,166};
Integer max = getMaxDigits(array);
Integer[] sortedArray = radixSortFunc(array,max,0);
for (Integer i = 0; i < sortedArray.length; i++){
if (sortedArray[i] != null){
System.out.println(sortedArray[i]);
}
else;
}
}
}
i am a begginer to java. i have made this code to sort an array using radix sort. when i run the code with any test array i get this error:
Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.lang.Integer.intValue()" because "array[java.lang.Integer.intValue()]" is null
at radixSort.radixSortFunc(radixSort.java:52)
at radixSort.radixSortFunc(radixSort.java:68)
at radixSort.main(radixSort.java:80)
i am a total begginer in java, so please dont tease me if i have made some noob mistake. it would also be helpful if you give me a shorter way to do this. for example lowering the number of functions.
It's because you call
return radixSortFunc(flatten(lsdArray),maxDigits,counter);
after the first loop.
lsdArray is an array almost full of null value (because you didn't initialize them in Integer[][] lsdArray = new Integer[10][15];).
So, when you pass in int term = (array[i] % powOfTen ); with array[i] = null you get a NPE.
By the way, you also have an issue with your getMaxDigits, it's not returning the maxlength element of your array.
for (int i = 0; i < array.length; i++){
m = Math.max(max, array[i]);
}
It's returning the length of the last element of your array. Instead you should do something like this
for (int i = 0; i < array.length; i++){
max = Math.max(max, array[i]);
m = max;
}
You might also remove var m and only use max if you want to optimize your function :)