Java Program for Pigeonhole Sort
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
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] + " " );
}
}
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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!
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