簡述

計數排序，就是統計某個數值在所有的數字中所應該存在的位置，然后，放到一個確定的位置上。非常簡單的排序算法。

程序

• 會讀取data.txt中的文件
• 數據的樣子

10 0 2 3 1 4 8 6 7 5 9

• 效果

PS D:\C++\VS\repo\OpenMP-TEST\Debug> ./OpenMP-TEST 0 1 2 3 4 5 6 7 8 9

• 代碼

#include <iostream> #include <omp.h> #include <fstream> using namespace std; #pragma warning(disable : 4996) int main(int argc, char **argv) {if (argc < 1) return 0;ifstream cin("./data.txt");int i, j, count, n;cin >> n;int *a = new int[n];int *temp = new int[n];//int thread_count = strtol(argv[1], NULL, 10);for (i = 0; i < n; ++i) cin >> a[i];#pragma omp parallel for private(i, j, count) shared(n, a, temp)for (i = 0; i < n; ++i) {count = 0;for (j = 0; j < n; ++j) {if (a[j] < a[i]) count++;else if (a[j] == a[i] && j < i) count++;}temp[count] = a[i];}#pragma omp parallel for for (i = 0; i < n; ++i) a[i] = temp[i];for (i = 0; i < n; ++i) cout << a[i]<< " ";cout << endl;delete[]temp;delete[]a; }

和串行的計數排序進行對比

• 不要輸出排序結果，因為數據量太大了。
• 10000個數據的排序效果

PS D:\C++\VS\repo\OpenMP-TEST\Debug> ./OpenMP-TEST r Total time Serial: 1.256s Total time parallel: 0.141s

• 接近9倍的速度（因為我在筆記本上有8個核）
• 后面多了一個r命令，其實是免得在vs編譯的時候被調用。隨便寫什么都是ok的。

#include <iostream> #include <omp.h> #include <fstream> #include <ctime> using namespace std; #pragma warning(disable : 4996) int main(int argc, char **argv) {if (argc < 2) return 0;ifstream cin("./data.txt");int i, j, count, n;cin >> n;int *a = new int[n];int *b = new int[n];int *temp = new int[n];//int thread_count = strtol(argv[1], NULL, 10);for (i = 0; i < n; ++i) cin >> b[i];for (i = 0; i < n; ++i) a[i] = b[i];clock_t starttime, endtime;starttime = clock();for (i = 0; i < n; ++i) {count = 0;for (j = 0; j < n; ++j) {if (b[j] < b[i]) count++;else if (b[j] == b[i] && j < i) count++;}temp[count] = b[i];}memcpy(b, temp, n * sizeof(int));endtime = clock();// for (i = 0; i < n; ++i) cout << b[i] << " ";// cout << endl;cout << "Total time Serial: " << (double)(endtime - starttime) / CLOCKS_PER_SEC << "s" << endl;starttime = clock(); #pragma omp parallel for private(i, j, count) shared(n, a, temp)for (i = 0; i < n; ++i) {count = 0;for (j = 0; j < n; ++j) {if (a[j] < a[i]) count++;else if (a[j] == a[i] && j < i) count++;}temp[count] = a[i];}#pragma omp parallel for for (i = 0; i < n; ++i) a[i] = temp[i];endtime = clock();//for (i = 0; i < n; ++i) cout << a[i]<< " ";//cout << endl;cout << "Total time parallel: " << (double)(endtime - starttime) / CLOCKS_PER_SEC << "s" << endl;delete[]temp;delete[]a;delete[]b; }

和qsort的串行版也做對比

#include <iostream> #include <omp.h> #include <fstream> #include <ctime> using namespace std; #pragma warning(disable : 4996) int cmp(const void * a, const void *b) //from small to big {return *(int *)a - *(int *)b; }int main(int argc, char **argv) {if (argc < 2) return 0;ifstream cin("./data.txt");int i, j, count, n;cin >> n;int *a = new int[n];int *b = new int[n];int *c = new int[n];int *temp = new int[n];//int thread_count = strtol(argv[1], NULL, 10);for (i = 0; i < n; ++i) cin >> b[i];for (i = 0; i < n; ++i) { a[i] = b[i]; c[i] = b[i]; }clock_t starttime, endtime;starttime = clock();qsort(c, n, sizeof(int), cmp);endtime = clock();cout << "Total time Serial-qsort: " << (double)(endtime - starttime) / CLOCKS_PER_SEC << "s" << endl;starttime = clock();for (i = 0; i < n; ++i) {count = 0;for (j = 0; j < n; ++j) {if (b[j] < b[i]) count++;else if (b[j] == b[i] && j < i) count++;}temp[count] = b[i];}memcpy(b, temp, n * sizeof(int));endtime = clock();cout << "Total time Serial: " << (double)(endtime - starttime) / CLOCKS_PER_SEC << "s" << endl;starttime = clock(); #pragma omp parallel for private(i, j, count) shared(n, a, temp)for (i = 0; i < n; ++i) {count = 0;for (j = 0; j < n; ++j) {if (a[j] < a[i]) count++;else if (a[j] == a[i] && j < i) count++;}temp[count] = a[i];}#pragma omp parallel for for (i = 0; i < n; ++i) a[i] = temp[i];endtime = clock();//for (i = 0; i < n; ++i) cout << a[i]<< " ";//cout << endl;cout << "Total time parallel: " << (double)(endtime - starttime) / CLOCKS_PER_SEC << "s" << endl;delete[]temp;delete[]a; }

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