bucketsort.cpp

/*bucketSort(arr[], n)
1) Create n empty buckets (Or lists).
2) Do following for every array element arr[i].
.......a) Insert arr[i] into bucket[n*array[i]]
3) Sort individual buckets using insertion sort.
4) Concatenate all sorted buckets.

*/

/*Time Complexity: If we assume that insertion in a bucket takes O(1) time then steps 1 and 2 of the above algorithm clearly take O(n) time. The O(1) is easily possible if we use a linked list to represent a bucket (In the following code, C++ vector is used for simplicity). Step 4 also takes O(n) time as there will be n items in all buckets. 
The main step to analyze is step 3. 
*/

// C++ program to sort an
// array using bucket sort
#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

// Function to sort arr[] of
// size n using bucket sort
void bucketSort(float arr[], int n)
{
	
	// 1) Create n empty buckets
	vector<float> b[n];

	// 2) Put array elements
	// in different buckets
	for (int i = 0; i < n; i++) {
		int bi = n * arr[i]; // Index in bucket
		b[bi].push_back(arr[i]);
	}

	// 3) Sort individual buckets
	for (int i = 0; i < n; i++)
		sort(b[i].begin(), b[i].end());

	// 4) Concatenate all buckets into arr[]
	int index = 0;
	for (int i = 0; i < n; i++)
		for (int j = 0; j < b[i].size(); j++)
			arr[index++] = b[i][j];
}

/* Driver program to test above function */
int main()
{
	float arr[]
		= { 0.897, 0.565, 0.656, 0.1234, 0.665, 0.3434 };
	int n = sizeof(arr) / sizeof(arr[0]);
	bucketSort(arr, n);

	cout << "Sorted array is \n";
	for (int i = 0; i < n; i++)
		cout << arr[i] << " ";
	return 0;
}