喵星人的星球

原文出處
程式人員的面試心得及基本原則

VB版程式碼，有另外加上執行時間的紀錄
以n = 100億
執行最初的那個程式碼用Pentium M 1.3GHz約390秒左右
跑偷吃步那個考官的算法
約....0.0005秒....

這是一開始作者的寫法(應該吧@@)

Module Module1

  Sub Main()
        Console.Write("請輸入n：")
        Dim n As Long
        Dim i As Long
        Dim Temp As Long
        Dim Flag As Integer = 1
        Dim Sum As Long
        Dim StartTime As Single
        Dim TotalTime As Single

        n = Console.ReadLine()
        StartTime = Timer

        For i = 1 To n
            Temp = Flag * i
            Flag = (-1) * Flag
            'Console.WriteLine(i)
            Sum = Sum + Temp
        Next

        TotalTime = Timer - StartTime
        Console.WriteLine(Format(TotalTime, "0.######"))
        Console.WriteLine(Sum)
        Console.Read()
  End Sub

End Module

===============

這是考官的寫法

Module Module1

  Sub Main()
        Console.Write("請輸入n：")
        Dim n As Long
        Dim Sum As Long
        Dim StartTime As Single
        Dim TotalTime As Single

        n = Console.ReadLine()
        StartTime = Timer

        If n Mod 2 = 0 Then
            Sum = (n / 2) * -1
        Else
            Sum = (n / 2) * -1 + n
        End If

        TotalTime = Timer - StartTime
        Console.WriteLine(Format(TotalTime, "0.######"))
        Console.WriteLine(Sum)
        Console.Read()

  End Sub

End Module