# Java Bitonic Sort Example

Write a Java program for Bitonic Sort algorithm.

# Java Bitonic Sort Example

```package net.sourcecodeexamples.java.sort;

/* Java program for Bitonic Sort. Note that this program
works only when size of input is a power of 2. */
public class BitonicSort {
/* The parameter dir 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 compAndSwap(int a[], int i, int j, int dir) {
if ((a[i] > a[j] && dir == 1) ||
(a[i] < a[j] && dir == 0)) {
// Swapping elements
int temp = a[i];
a[i] = a[j];
a[j] = temp;
}
}

/* It recursively sorts a bitonic sequence in ascending
order, if dir = 1, and in descending order otherwise
(means dir=0). The sequence to be sorted starts at
index position low, the parameter cnt is the number
of elements to be sorted.*/
void bitonicMerge(int a[], int low, int cnt, int dir) {
if (cnt > 1) {
int k = cnt / 2;
for (int i = low; i < low + k; i++)
compAndSwap(a, i, i + k, dir);
bitonicMerge(a, low, k, dir);
bitonicMerge(a, low + k, k, dir);
}
}

/* This funcion 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 */
void bitonicSort(int a[], int low, int cnt, int dir) {
if (cnt > 1) {
int k = cnt / 2;

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

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

// Will merge wole sequence in ascending order
// since dir=1.
bitonicMerge(a, low, cnt, dir);
}
}

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

public static void main(String args[]) {
int a[] = {
3,
7,
4,
8,
6,
2,
1,
5
};
int up = 1;
System.out.println("\nBefore Sorted array");
printArray(a);
BitonicSort ob = new BitonicSort();
ob.sort(a, a.length, up);
System.out.println("\nAfter Sorted array");
printArray(a);
}
}```

## Output

``````
Before Sorted array
3 7 4 8 6 2 1 5

After Sorted array
1 2 3 4 5 6 7 8 ``````