Java Program for Pigeonhole Sort (original) (raw)

Last Updated : 18 Oct, 2023

Pigeonhole sorting is a sorting algorithm that is suitable for sorting lists of elements where the number of elements and the number of possible key values are approximately the same.
It requires O(n + Range) time where n is the number of elements in the input array and ‘Range’ is the number of possible values in the array.

**Step-by-step approach:

• Find minimum and maximum values in the array. Let the minimum and maximum values be ‘min’ and ‘max’ respectively. Also, find the range as ‘max-min+1’.
• Set up an array of initially empty “pigeonholes” the same size as the range.
• Visit each element of the array and then put each element in its pigeonhole. An element arr[i] is put in the hole at index arr[i] – min.
• Start the loop all over the pigeonhole array in order and put the elements from non-empty holes back into the original array.

**Comparison with Counting Sort :
It is similar to counting sort, but differs in that it“moves items twice: once to the bucket array and again to the final destination “.

Below is the implementation of the above approach:

Java `

/* Java program to implement Pigeonhole Sort */

import java.lang.; import java.util.;

public class GFG { public static void pigeonhole_sort(int arr[], int n) { int min = arr[0]; int max = arr[0]; int range, i, j, index;

    for (int a = 0; a < n; a++) {
        if (arr[a] > max)
            max = arr[a];
        if (arr[a] < min)
            min = arr[a];
    }

    range = max - min + 1;
    int[] phole = new int[range];
    Arrays.fill(phole, 0);

    for (i = 0; i < n; i++)
        phole[arr[i] - min]++;

    index = 0;

    for (j = 0; j < range; j++)
        while (phole[j]-- > 0)
            arr[index++] = j + min;
}

public static void main(String[] args)
{
    GFG sort = new GFG();
    int[] arr = { 8, 3, 2, 7, 4, 6, 8 };

    System.out.print("Sorted order is : ");

    sort.pigeonhole_sort(arr, arr.length);

    for (int i = 0; i < arr.length; i++)
        System.out.print(arr[i] + " ");
}

}

// Code contributed by Mohit Gupta_OMG <(0_o)>

`

Output

Sorted order is : 2 3 4 6 7 8 8

**Time complexity: O(n + range), where n is the number of elements in the array and range is the range of the input data.
**Auxiliary space: O(range)

**Advantages of Pigeonhole sort:

• It is a non-comparison based sort making it faster in application.
• It is a stable sorting algorithm.
• It performs sorting in linear time.

**Disadvantages of Pigeonhole sort:

• It is not easy to know the range of the numbers to sort.
• This number might only work with zero and positive integers.
• Pigeonhole Sort

Please refer to the complete article on Pigeonhole Sort for more details!