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Added bitonic sort #244

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86 changes: 86 additions & 0 deletions Sorts/BitonicSort.java
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public class BitonicSort {
/**
* The parameter sortingDirection indicates the sorting direction, ASCENDING or
* DESCENDING; if (a[i] > a[j]) agrees with the direction, then a[i] and
* a[j] are interchanged.
*/
void compareAndSwap(int arr[], int i, int j, int sortingDirection) {
if ((arr[i] > arr[j] && sortingDirection == 1) || (arr[i] < arr[j] && sortingDirection == 0)) {
// Swapping elements
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}

/**
* This function is being called to merge two sorted arrays in same order.
*
* @param arr - array to be sorted
* @param low - starting index position of the sequence to be sorted
* @param noOfEleToBeSorted - Number of elements to be sorted
* @param sortingDirection - 0 -> ascending direction, 1 -> descending direction
*/
void bitonicMerge(int arr[], int low, int noOfEleToBeSorted, int sortingDirection) {
if (noOfEleToBeSorted > 1) {
int k = noOfEleToBeSorted / 2;
for (int i = low; i < low + k; i++)
compareAndSwap(arr, i, i + k, sortingDirection);
bitonicMerge(arr, low, k, sortingDirection);
bitonicMerge(arr, low + k, k, sortingDirection);
}
}

/**
* This function first produces a bitonic sequence by recursively sorting its
* two halves in opposite sorting orders, and then calls bitonicMerge to
* make them in the same order
*
* @param arr - array to be sorted
* @param low - starting index position of the sequence to be sorted
* @param noOfEleToBeSorted - Number of elements to be sorted
* @param sortingDirection - 0 -> ascending direction, 1 -> descending direction
*/
void bitonicSort(int arr[], int low, int noOfEleToBeSorted, int sortingDirection) {
if (noOfEleToBeSorted > 1) {
int k = noOfEleToBeSorted / 2;

// sort in ascending order since sortingDirection here is 1
bitonicSort(arr, low, k, 1);

// sort in descending order since sortingDirection here is 0
bitonicSort(arr, low + k, k, 0);

// Will merge whole sequence in ascending order
// since sortingDirection=1.
bitonicMerge(arr, low, noOfEleToBeSorted, sortingDirection);
}
}

/**
* Caller of bitonicSort for sorting the entire array of length N in
* ASCENDING order
*/
void sort(int arr[], int N, int up) {
bitonicSort(arr, 0, N, up);
}

/* A utility function to print array of size n */
static void printArray(int arr[]) {
int n = arr.length;
for (int i = 0; i < n; ++i)
System.out.print(arr[i] + " ");
System.out.println();
}

// Driver method
public static void main(String args[]) {
int arr[] = { 3, 7, 4, 8, 6, 2, 1, 5 };
int up = 1;
BitonicSort ob = new BitonicSort();
ob.sort(arr, arr.length, up);
System.out.println("\nSorted array");
printArray(arr);
}
}