我试图确定 C# 中迭代或递归更快。然而，在一个简单的测试中，我似乎无法使用 StopWatch 获得可靠的结果。
代码：
internal class Program
{
// The factorial of a number is the product of all the
// integers from 1 to that number.
// For example, the factorial of 6 is 1*2*3*4*5*6 = 720
// Factorial is not defined for negative numbers, and the factorial of zero is one, 0! = 1
static void Main(string[] args)
{
Console.WriteLine("Please Enter a Number:");
//read number from user
int number = Convert.ToInt32(Console.ReadLine());
double sw1Elapsed = 0d;
double sw2Elapsed = 0d;
double factorial = 0d;
double factorial2 = 0d;
Stopwatch sw = new Stopwatch();
sw.Reset();
for (int i = 0; i < 6; i++)
{
sw.Restart();
factorial = Factorial(number);
sw.Stop();
sw1Elapsed = sw1Elapsed + sw.Elapsed.TotalMilliseconds;
sw.Restart();
factorial2 = FactorialByRecursion(number);
sw.Stop();
sw2Elapsed = sw2Elapsed + sw.Elapsed.TotalMilliseconds;
//print the factorial result
Console.WriteLine("Iteration:");
Console.WriteLine("Factorial of " + number + " = " + factorial.ToString());
Console.WriteLine("Iteration Time taken = " + sw1Elapsed);
Console.WriteLine();
Console.WriteLine("Recursion:");
Console.WriteLine("Factorial of " + number + " = " + factorial2.ToString());
Console.WriteLine("Recursion Time taken = " + sw2Elapsed);
Console.WriteLine("-----------------------------------------------------\n");
}
}
public static double Factorial(int number)
{
if (number == 0)
return 1;
double factorial = 1;
for (int i = number; i >= 1; i--)
{
factorial = factorial * i;
}
return factorial;
}
public static double FactorialByRecursion(int number)
{
if (number == 0)
return 1;
return number * FactorialByRecursion(number - 1);//Recursive call
}
}
}
所以有两个函数以两种不同的方式做同样的事情。
这些产生了这些结果：
Please Enter a Number: 6 Iteration: Factorial of 6 = 720 Iteration Time taken = 0.3171
Recursion: Factorial of 6 = 720 Recursion Time taken = 0.0616
-----------------------------------------------------
Iteration: Factorial of 6 = 720 Iteration Time taken = 0.3172
Recursion: Factorial of 6 = 720 Recursion Time taken =
0.061700000000000005
-----------------------------------------------------
Iteration: Factorial of 6 = 720 Iteration Time taken =
0.31739999999999996
Recursion: Factorial of 6 = 720 Recursion Time taken =
0.06180000000000001
-----------------------------------------------------
Iteration: Factorial of 6 = 720 Iteration Time taken =
0.31749999999999995
Recursion: Factorial of 6 = 720 Recursion Time taken =
0.06190000000000001
-----------------------------------------------------
Iteration: Factorial of 6 = 720 Iteration Time taken =
0.31759999999999994
Recursion: Factorial of 6 = 720 Recursion Time taken =
0.06200000000000001
-----------------------------------------------------
Iteration: Factorial of 6 = 720 Iteration Time taken =
0.3177999999999999
Recursion: Factorial of 6 = 720 Recursion Time taken =
0.062100000000000016
-----------------------------------------------------
C:\Users\Dev\source\repos\SimpleRecursion\SimpleRecursion\bin\Debug\net6.0\SimpleRecursion.exe (process 26992) exited with code 0. To automatically close the console when debugging stops, enable Tools->Options->Debugging->Automatically close the console when debugging stops. Press any key to close this window . . .
但是，如果我将第二个函数移动到循环中第一个函数的上方，那么可能是：
static void Main(string[] args)
{
Console.WriteLine("Please Enter a Number:");
//read number from user
int number = Convert.ToInt32(Console.ReadLine());
double sw1Elapsed = 0d;
double sw2Elapsed = 0d;
double factorial = 0d;
double factorial2 = 0d;
Stopwatch sw = new Stopwatch();
sw.Reset();
for (int i = 0; i < 6; i++)
{
sw.Restart();
factorial2 = FactorialByRecursion(number);
sw.Stop();
sw2Elapsed = sw2Elapsed + sw.Elapsed.TotalMilliseconds;
sw.Restart();
factorial = Factorial(number);
sw.Stop();
sw1Elapsed = sw1Elapsed + sw.Elapsed.TotalMilliseconds;
//print the factorial result
Console.WriteLine("Iteration:");
Console.WriteLine("Factorial of " + number + " = " + factorial.ToString());
Console.WriteLine("Iteration Time taken = " + sw1Elapsed);
Console.WriteLine();
Console.WriteLine("Recursion:");
Console.WriteLine("Factorial of " + number + " = " + factorial2.ToString());
Console.WriteLine("Recursion Time taken = " + sw2Elapsed);
Console.WriteLine("-----------------------------------------------------\n");
}
}
那么结果就变成：
Please Enter a Number:
6
Iteration:
Factorial of 6 = 720
Iteration Time taken = 0.0571
Recursion:
Factorial of 6 = 720
Recursion Time taken = 0.1066
-----------------------------------------------------
Iteration:
Factorial of 6 = 720
Iteration Time taken = 0.0571
Recursion:
Factorial of 6 = 720
Recursion Time taken = 0.1069
-----------------------------------------------------
Iteration:
Factorial of 6 = 720
Iteration Time taken = 0.0572
Recursion:
Factorial of 6 = 720
Recursion Time taken = 0.1071
-----------------------------------------------------
Iteration:
Factorial of 6 = 720
Iteration Time taken = 0.0572
Recursion:
Factorial of 6 = 720
Recursion Time taken = 0.1073
-----------------------------------------------------
Iteration:
Factorial of 6 = 720
Iteration Time taken = 0.0572
Recursion:
Factorial of 6 = 720
Recursion Time taken = 0.10750000000000001
-----------------------------------------------------
Iteration:
Factorial of 6 = 720
Iteration Time taken = 0.057300000000000004
Recursion:
Factorial of 6 = 720
Recursion Time taken = 0.10770000000000002
-----------------------------------------------------
C:\Users\Dev\source\repos\SimpleRecursion\SimpleRecursion\bin\Debug\net6.0\SimpleRecursion.exe (process 26100) exited with code 0.
To automatically close the console when debugging stops, enable Tools->Options->Debugging->Automatically close the console when debugging stops.
Press any key to close this window . . .
谁能解释一下经过时间的差异以及为什么/发生了什么？
评论中已经提到了，但是使用基准测试工具来处理这样的事情；例如https://benchmarkdotnet.org/