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package com.sorts;
public class PigeonholeSort {
/**
* This method sorts the array using Pigeonhole sort technique.
* <p>
* Pigeonhole sorting is a sorting algorithms that is suitable for sorting lists of elements where the number
* of elements and the number of possible key values are approximately the same.
* <p>
* It requires O(n + Range) time where n is number of elements in input array and ‘Range’ is number of possible
* values in array.
*
* @param arr The array to be sorted
* @return arr Sorted array
*/
public Integer[] sort(Integer[] arr) {
// Find maximum and minimum elements in array
int min = Integer.MAX_VALUE;
int max = Integer.MIN_VALUE;
for (Integer integer : arr) {
min = Math.min(min, integer);
max = Math.max(max, integer);
}
// Range
int range = max - min + 1;
// Pigeonhole array
int[] pigeonholes = new int[range];
// Put each element of arr in its pigeonhole
for (Integer integer : arr) {
// This increment operation will count for the duplicates elements, if present
pigeonholes[integer - min]++;
}
// Index for the original array
int index = 0;
// Loop over pigeonhole array
for (int i = 0; i < range; i++) {
// This inner loop will execute only for those indexes in
// pigeonhole which are greater than zero i.e., only for those
// elements which are present in the original array. This also
// takes care of the duplicate elements
while (pigeonholes[i]-- > 0) {
arr[index++] = i + min;
}
}
return arr;
}
}