我一直试图让这段代码在几天内变得更快,更有效,但它似乎仍然没有那么高效。
Sub Main()
Dim watch As Stopwatch = Stopwatch.StartNew()
Dim l As New List(Of ULong)(CType(My.Application.CommandLineArgs.Item(0), ULong))
For i As ULong = 1 To l.Capacity
' ONE LINE IF STMT: If l.Capacity And 1 <> 0 Then If i And 1 = 0 Then l.Add((i * i) - 1) Else l.Add((i * i) + 1) Else If i And 1 = 0 Then l.Add((i * i) + 1) Else l.Add((i * i) - 1)
If l.Capacity And 1 <> 0 Then
If i And 1 = 0 Then
l.Add((i * i) - 1)
Else
l.Add((i * i) + 1)
End If
Else
If i And 1 = 0 Then
l.Add((i * i) + 1)
Else
l.Add((i * i) - 1)
End If
End If
Next i
Console.WriteLine(String.Join(","c, l.ToArray))
watch.Stop()
Console.WriteLine(watch.Elapsed.TotalMilliseconds)
Console.ReadLine()
End Sub
它目前在4.3毫秒内运行100次迭代。 我觉得嵌套的if语句是这里的主要瓶颈,但我不确定我是否可以改变它们。
那么,这段代码可以提高效率吗?
谢谢...:)
答案 0 :(得分:1)
首先,将If l.Capacity And 1 <> 0
拉出循环,因为它总是一样。
然后,删除位操作以支持更可读的i Mod 2 = 0
测试:您似乎认为这更有效,但实际上这些简单的优化最好留给编译器和运行时,它们没有位置在你的代码中,我严重怀疑他们有任何可衡量的影响。
如果仍然效率低下,请不要使用初始容量和Add
。相反,使用Resize
和索引访问元素。然后你也可以通过使用两个循环去除其他If
语句:一个用于偶数元素,一个用于奇数元素。
那就是说, Join
操作可能是迄今为止最慢的步骤(除了实际打印到控制台之外),你无能为力优化。
最后,我发现CType
非常难以理解:你在这里做的不是演员 - 这是解析操作。为什么不把它写成一个呢? ULong.Parse(…)
。另外,为什么你使用笨拙的My.Application.CommandLineArgs.Item
而不是接受命令行参数作为Main
的参数?
答案 1 :(得分:0)
一旦我只纠正了你的错误,就像我认为的那样,我在使用带有版本构建的Visual Studio 2010的Ctrl + F5时得到了这个输出:
0,5,8,17,24,37,48,65,80,101,120,145,168,197,224,257,288,325,360,401,440,485,528,577,624,677,728,785,840,901,960,1025,1088,1157,1224,1297,1368,1445,1520,1601,1680,1765,1848,1937,2024,2117 ,2208,2305,2400,2501,2600,2705,2808,2917,3024,3137,3248,3365,3480,3601,3720,3845,3968,4097,4224,4357,4488,4625,4760,4901,5040 ,5185,5328,5477,5624,5777,5928,6085,6240,6401,6560,6725,6888,7057,7224,7397,7568,7745,7920,8101,8280,8465,8648,8837,9024,9217 ,9408,9605,9800,10001
33.9106
这是代码:
Sub Main()
Dim watch As Stopwatch = Stopwatch.StartNew()
Dim l As New List(Of ULong)(CInt(My.Application.CommandLineArgs(0)))
For i As ULong = 1 To CULng(l.Capacity)
' ONE LINE IF STMT: If l.Capacity And 1 <> 0 Then If i And 1 = 0 Then l.Add((i * i) - 1) Else l.Add((i * i) + 1) Else If i And 1 = 0 Then l.Add((i * i) + 1) Else l.Add((i * i) - 1)
If (l.Capacity And 1) <> 0 Then
If (i And 1UL) = 0UL Then
l.Add((i * i) - 1UL)
Else
l.Add((i * i) + 1UL)
End If
Else
If (i And 1UL) = 0UL Then
l.Add((i * i) + 1UL)
Else
l.Add((i * i) - 1UL)
End If
End If
Next i
Console.WriteLine(String.Join(","c, l.ToArray))
watch.Stop()
Console.WriteLine(watch.Elapsed.TotalMilliseconds)
Console.ReadLine()
End Sub
使用LINQ:
0,5,8,17,24,37,48,65,80,101,120,145,168,197,224,257,288,325,360,401,440,485,528,577,624,677,728,785,840,901,960,1025,1088,1157,1224,1297,1368,1445,1520,1601,1680,1765,1848,1937,2024,2117 ,2208,2305,2400,2501,2600,2705,2808,2917,3024,3137,3248,3365,3480,3601,3720,3845,3968,4097,4224,4357,4488,4625,4760,4901,5040 ,5185,5328,5477,5624,5777,5928,6085,6240,6401,6560,6725,6888,7057,7224,7397,7568,7745,7920,8101,8280,8465,8648,8837,9024,9217 ,9408,9605,9800,10001
13.0721
那是:
Sub Main()
Dim watch As Stopwatch = Stopwatch.StartNew()
Dim arg = CInt(My.Application.CommandLineArgs(0))
Console.WriteLine(String.Join(","c, Enumerable.Range(1, arg).Select(
Function(i) ((i * i +
If((arg And 1) <> 0,
If((i And 1) = 0, -1, 1),
If((i And 1) = 0, 1, -1))).ToString()))))
watch.Stop()
Console.WriteLine(watch.Elapsed.TotalMilliseconds)
Console.ReadLine()
End Sub
现已优化:
0,5,8,17,24,37,48,65,80,101,120,145,168,197,224,257,288,325,360,401,440,485,528,577,624,677,728,785,840,901,960,1025,1088,1157,1224,1297,1368,1445,1520,1601,1680,1765,1848,1937,2024,2117 ,2208,2305,2400,2501,2600,2705,2808,2917,3024,3137,3248,3365,3480,3601,3720,3845,3968,4097,4224,4357,4488,4625,4760,4901,5040 ,5185,5328,5477,5624,5777,5928,6085,6240,6401,6560,6725,6888,7057,7224,7397,7568,7745,7920,8101,8280,8465,8648,8837,9024,9217 ,9408,9605,9800,10001
12.5956
在这一点上,我认为我明显地在时间范围内点击Console.WriteLine
方差,但即使使用下面的代码,我仍然会得到12到15毫秒......
Sub Main()
Dim watch As Stopwatch = Stopwatch.StartNew()
Dim arg = CInt(My.Application.CommandLineArgs(0))
Dim fn As Func(Of Integer, String) = If((arg And 1) <> 0,
Function(i As Integer) ((i * i + If((i And 1) = 0, -1, 1)).ToString()),
Function(i As Integer) ((i * i + If((i And 1) = 0, 1, -1)).ToString()))
Dim s = String.Join(","c, Enumerable.Range(1, arg).Select(fn))
watch.Stop()
Console.WriteLine(s)
Console.WriteLine(watch.Elapsed.TotalMilliseconds)
Console.ReadLine()
End Sub