Bucket sort (Java)

From LiteratePrograms

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Bucket sort is possibly the simplest distribution sorting algorithm. The essential requirement is that the size of the array from which the elements to be sorted are drawn is a small, fixed constant, say n.

<<sort function>>=
public static int[] bucketSort(int[] arr) {
  int i, j;
  int[] count = new int[arr.length];
  count amount of each array-number
  rearrange order of array
  return arr;
}

For example, suppose that we are sorting elements drawn from {0, 1, . . ., n-1}. The integers in this set can be of the range 0 until (n-1). The elements of an integer array are initialized to 0 when created.

To we can determine the amount of each number in the array we want to sort.

<<count amount of each array-number>>=
for(i = 0; i < arr.length; i++ ) {
  count[arr[i]]++;
}

After we've determined all needed information about the array we want to sort. The array can be sorted. j holds the current position in the array to sort. i holds the current position in the counter array,

<<rearrange order of array>>=
for(i=0,j=0; i < count.length; i++) {
  for(; count[i]>0; (count[i])--) {
    arr[j++] = i;
  }
}

Putting it together

To check the bucket sort, we output the data:

<<output the array>>=
for(int i = 0; i < arr.length; i++ ) {
  System.out.print(arr[i] + " ");
}
System.out.println();

Putting it all together with a example array.

<<Bucketsort.java>>=
import java.util.Arrays;
public class Bucketsort {
  sort function
  public static void main(String[] args) {
    int[] arr = new int[] {1,3,4,6,4,2,9,1,2,9};
    output the array
    arr = bucketSort(arr);
    output the array
  }
}

This generates following output:

1 3 4 6 4 2 9 1 2 9 
1 1 2 2 3 4 4 6 9 9