Introduction

The pigeonhole sorting algorithm is used where number of elements and number of key value will be approximately same.

Program

def sort(ip_arr):
    arr_min = min(ip_arr)
    arr_max = max(ip_arr)
    arr_size = arr_max - arr_min + 1
    holes = [0] * arr_size
    for x in ip_arr:
        assert type(x) is int, "integers only"
        holes[x - arr_min] += 1
    i = 0
    for j in range(arr_size):
        while holes[j] > 0:
            holes[j] -= 1
            ip_arr[i] = j + arr_min
            i += 1


ip_arr = [54, 26, 81, 1]
sort(ip_arr)
print("The sorted array is :")
for i in range(len(ip_arr)):
    print(ip_arr[i])

Output

Explanation

The above code follows the following steps:

• We have maximum and minimum values in the array. From max and min values we will calculate the range max – (min + 1).
• Construct the array of size range that we have calculated.
• Traverse through the elements of array, and place it at index arr[i] – min.
• When all the elements are sorted in the new pigeonhole array, traverse through all the elements of pigeonhole array in order and place it back to the original array.
• Return the array with sorted elements.