C++ 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:
C++
#include <bits/stdc++.h>
using namespace std;
void pigeonholeSort( int arr[], int n)
{
int min = arr[0], max = arr[0];
for ( int i = 1; i < n; i++) {
if (arr[i] < min)
min = arr[i];
if (arr[i] > max)
max = arr[i];
}
int range = max - min + 1;
vector< int > holes[range];
for ( int i = 0; i < n; i++)
holes[arr[i] - min].push_back(arr[i]);
int index = 0;
for ( int i = 0; i < range; i++) {
vector< int >::iterator it;
for (it = holes[i].begin(); it != holes[i].end();
++it)
arr[index++] = *it;
}
}
int main()
{
int arr[] = { 8, 3, 2, 7, 4, 6, 8 };
int n = sizeof (arr) / sizeof (arr[0]);
pigeonholeSort(arr, n);
printf ( "Sorted order is : " );
for ( int i = 0; i < n; i++)
printf ( "%d " , arr[i]);
return 0;
}
|
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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