C program for Pigeonhole sort algorithm : **Pigeonhole sorting**, also known as **count sort** (not to be confused with counting sort), is a sorting algorithm that is suitable for sorting lists of elements where the number of elements (*n*) and the number of possible key values (*N*) are approximately the same.^{
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**The pigeonhole algorithm works as follows**:

- Given an array of values to be sorted, set up an auxiliary array of initially empty “pigeonholes,” one pigeonhole for each key through the range of the original array.
- Going over the original array, put each value into the pigeonhole corresponding to its key, such that each pigeonhole eventually contains a list of all values with that key.
- Iterate over the pigeonhole array in order, and put elements from non-empty pigeonholes back into the original array.

Now let us see how to write a **C program for Pigeonhole Sort Algorithm** which accepts number of elements and their values from user and generates the output file using pigeon sort.

### C program for Pigeonhole Sort Algorithm :

#include<stdio.h> #include<conio.h> #include<stdlib.h> void pigeonhole_sort(int arr[], int num, int min, int max) { int size,i,j,k,count; size = max - min + 1; // array of pigeonholes int holes[size]; for(i=0;i<size;i++) { holes[i]=0; } // Populate the pigeonholes. for (j=0; j < num ;j++) holes[arr[j] - min]++; // Put the elements back into the array in order. k=0; for (count = 0; count < size; count++) while (holes[count]-- > 0) { arr[k] = count + min; k=k+1; } } int main() { int i,n, array[100], c, d, t,min,max, flag=0; printf("-----------------------------------------------------------\n"); printf("----------------------Made by C code champ-----------------\n"); printf("-----------------------------------------------------------\n\n"); printf("\t\tPIGEONHOLE SORT ALGORITHM\n\n\n\n"); printf("Enter the number of input : "); scanf("%d",&n); printf("Enter the smallest value in the list: "); scanf("%d",&min); printf("Enter the largest number in the list : "); scanf("%d",&max); printf("\n\nEnter the elements to be sorted :\n"); for ( i = 0; i < n; i++) { scanf("%d",&array[i]); if(array[i]<min && array[i]>max) { printf("\nEntered Element : %d is out of range \n",array[i]); getch(); return 0; } } for(i=0;i<n;i++) { if(array[i]<min || array[i]>max) { printf("\nEntered Element : %d is out of range \n",array[i]); flag=1; } } if(flag==1) { printf("\nEnter the elements correctly within %d and %d range\n",min,max); } if(flag==0) { pigeonhole_sort(array, n,min,max); printf("\n\nSorted List by Pigeonhole Sort :\n"); for ( i = 0; i < n; i++) { printf("%d\t",array[i]); } } getch(); return 0; }

We hope you all have enjoyed the **C program** of Pigeonhole sort algorithm. If you have any issues with above code, let us know in form of comments.

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