pigeonholesort.go

// Pigeonhole algorithm's working at wikipedia.
// https://en.wikipedia.org/wiki/Pigeonhole_sort
// time complexity: O(n + N) where n is the number of elements in the array and N is the range of input
// space complexity: O(N)

package sort

import (
	"github.com/TheAlgorithms/Go/constraints"
	"github.com/TheAlgorithms/Go/math/max"
	"github.com/TheAlgorithms/Go/math/min"
)

// Pigeonhole sorts a slice using pigeonhole sorting algorithm.
// NOTE: To maintain time complexity O(n + N), this is the reason for having
// only Integer constraint instead of Ordered.
func Pigeonhole[T constraints.Integer](arr []T) []T {
	if len(arr) == 0 {
		return arr
	}

	max := max.Int(arr...)
	min := min.Int(arr...)

	size := max - min + 1

	holes := make([]T, size)

	for _, element := range arr {
		holes[element-min]++
	}

	i := 0

	for j := T(0); j < size; j++ {
		for holes[j] > 0 {
			holes[j]--
			arr[i] = j + min
			i++
		}
	}

	return arr
}