Odd-Even Transposition Sort is a parallel sorting algorithm. It is based on the Bubble Sort technique, which compares every 2 consecutive numbers in the array and swap them if first is greater than the second to get an ascending order array. It consists of 2 phases – the odd phase and even phase:
- Odd phase: Every odd indexed element is compared with the next even indexed element(considering 1-based indexing).
- Even phase: Every even indexed element is compared with the next odd indexed element.
This article uses the concept of multi-threading, specifically pthread. In each iteration, every pair of 2 consecutive elements is compared using individual threads executing in parallel as illustrated below.
Examples:
Input: { 2, 1, 4, 9, 5, 3, 6, 10 } Output: 1, 2, 3, 4, 5, 6, 9, 10 Input: { 11, 19, 4, 20, 1, 22, 25, 8} Output: 1, 4, 8, 11, 19, 20, 22, 25
Note: Compile the program using following command on your Linux based system.
g++ program_name.cpp -pthread
Below is the implementation of the above topic:
// CPP Program for Odd-Even Transpostion sort // using pthreads #include <bits/stdc++.h> #include <pthread.h> using namespace std; // size of array #define n 8 // maximum number of threads int max_threads = (n + 1) / 2; int a[] = { 2, 1, 4, 9, 5, 3, 6, 10 }; int tmp; // Function to compare and exchange // the consecutive elements of the array void * compare( void * arg) { // Each thread compares // two consecutive elements of the array int index = tmp; tmp = tmp + 2; if ((a[index] > a[index + 1]) && (index + 1 < n)) { swap(a[index], a[index + 1]); } } void oddEven(pthread_t threads[]) { int i, j; for (i = 1; i <= n; i++) { // Odd step if (i % 2 == 1) { tmp = 0; // Creating threads for (j = 0; j < max_threads; j++) pthread_create(&threads[j], NULL, compare, NULL); // joining threads i.e. waiting // for all the threads to complete for (j = 0; j < max_threads; j++) pthread_join(threads[j], NULL); } // Even step else { tmp = 1; // Creating threads for (j = 0; j < max_threads - 1; j++) pthread_create(&threads[j], NULL, compare, NULL); // joining threads i.e. waiting // for all the threads to complete for (j = 0; j < max_threads - 1; j++) pthread_join(threads[j], NULL); } } } // Function to print an array void printArray() { int i; for (i = 0; i < n; i++) cout << a[i] << " " ; cout << endl; } // Driver Code int main() { pthread_t threads[max_threads]; cout << "Given array is: " ; printArray(); oddEven(threads); cout << "\nSorted array is: " ; printArray(); return 0; } |
Output:
Given array is: 2 1 4 9 5 3 6 10 Sorted array is: 1 2 3 4 5 6 9 10
Time complexity: The time complexity is reduced to O(N) due to parallel computation using threads.
Work complexity: The work complexity of this program is O(N) as N/2 number of threads(resources) are being used to sort the array. So, the work-time complexity of the program is O(N^2).
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