项目中需要大量计算9个数中取最小值，现在测试一下几种方法的速度。
软件环境VC 6.0 + Windows xp sp3;
硬件环境 Pentium G630 双核 2.7GHz，3GB内存。
第一种方法：#define min(a,b) a<b?a:b
#include <iostream.h> #include <TIME.H> #define min(a,b) a<b?a:b #include <stdlib.h> int main() { clock_t start, finish; long duration; int minimum_in9 = 0; int array[9]; srand((unsigned)time(0)); for(int i=0;i<9;i++) { array[i]=rand() % 100; cout<<array[i]<<" "; } cout<<"\n"; start = clock(); for (int t=0;t<100000000;t++) { int a1 = min(array[0],array[1]); int a2 = min(array[2],array[3]); int a3 = min(array[4],array[5]); int a4 = min(array[6],array[7]); int b1 = min(a1,a2); int b2 = min(a3,a4); int c1 = min(b1,b2); minimum_in9 = min(c1,array[8]); } finish = clock(); cout<<"minimum_in9 = "<<minimum_in9<<"\n"; duration = (long)(finish-start); cout<<"total time is = "<<duration<<" milliseconds"<<endl; return 1; }
这种方法在1亿次循环中，耗时大约1100毫秒(1068~1170)。
第二种方法：使用二维矩形循环比较
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#include <iostream.h> #include <TIME.H> #include <stdlib.h> int main() { clock_t start, finish; long duration; int minimum_in9; int array[9]; srand((unsigned)time(0)); for(int i=0;i<9;i++) { array[i]=rand() % 100; cout<<array[i]<<" "; } cout<<"\n"; start = clock(); for (int t=0;t<100000000;t++) { minimum_in9 = 0; for (int i=0;i<3;i++) { for (int j=0;j<3;j++) { int temp = array[i*3+j]; minimum_in9 = (minimum_in9<temp)?temp:minimum_in9; } } } finish = clock(); cout<<"minimum_in9 = "<<minimum_in9<<"\n"; duration = (long)(finish-start); cout<<"total time is = "<<duration<<" milliseconds"<<endl; return 1; }
这种方法在1亿次循环中，耗时大约3650毫秒(3578~3687)。
第三种方法：使用一维矩形循环比较
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#include <iostream.h> #include <TIME.H> #include <stdlib.h> int main() { clock_t start, finish; long duration; int minimum_in9; int array[9]; srand((unsigned)time(0)); for(int i=0;i<9;i++) { array[i]=rand() % 100; cout<<array[i]<<" "; } cout<<"\n"; start = clock(); for (int t=0;t<100000000;t++) { minimum_in9 = 0; for (int i=0;i<9;i++) { minimum_in9 = (minimum_in9<array[i])?array[i]:minimum_in9; } } finish = clock(); cout<<"minimum_in9 = "<<minimum_in9<<"\n"; duration = (long)(finish-start); cout<<"total time is = "<<duration<<" milliseconds"<<endl; return 1; }
这种方法在1亿次循环中，耗时大约2800毫秒(2734~2859)。
第四种方法：将第一种方法改为调用函数
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#include <iostream.h> #include <TIME.H> #include <stdlib.h> min(int a,int b); int main() { clock_t start, finish; long duration; int minimum_in9 = 0; int array[9]; srand((unsigned)time(0)); for(int i=0;i<9;i++) { array[i]=rand() % 100; cout<<array[i]<<" "; } cout<<"\n"; start = clock(); for (int t=0;t<100000000;t++) { int a1 = min(array[0],array[1]); int a2 = min(array[2],array[3]); int a3 = min(array[4],array[5]); int a4 = min(array[6],array[7]); int b1 = min(a1,a2); int b2 = min(a3,a4); int c1 = min(b1,b2); minimum_in9 = min(c1,array[8]); } finish = clock(); cout<<"minimum_in9 = "<<minimum_in9<<"\n"; duration = (long)(finish-start); cout<<"total time is = "<<duration<<" milliseconds"<<endl; return 1; } int min(int a,int b) { return a<b?a:b; }
这种方法在1亿次循环中，耗时大约13800毫秒(13718~13937)。
第五种方法：调用函数比较
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#include <iostream.h> #include <TIME.H> #include <stdlib.h> int min(int a, int b, int c); int main() { clock_t start, finish; long duration; int minimum_in9 = 0; int array[9]; srand((unsigned)time(0)); for(int i=0;i<9;i++) { array[i]=rand() % 100; cout<<array[i]<<" "; } cout<<"\n"; start = clock(); for (int t=0;t<100000000;t++) { int b1 = min(array[0],array[1],array[2]); int b2 = min(array[3],array[4],array[5]); int b3 = min(array[6],array[7],array[8]); minimum_in9 = min(b1, b2, b3); } finish = clock(); cout<<"minimum_in9 = "<<minimum_in9<<"\n"; duration = (long)(finish-start); cout<<"total time is = "<<duration<<" milliseconds"<<endl; return 1; } int min(int a, int b, int c) { if(a>b) a=b; if(a>c) a=c; return a; }
这种方法在1亿次循环中，耗时大约7000毫秒(6906~7031)。