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)> |
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!
Ready to dive in? Explore our Free Demo Content and join our DSA course, trusted by over 100,000 neveropen!
