一道面试题, 求 1000!的位数(VBS实现)

王朝vb·作者佚名  2006-01-27
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http://community.csdn.net//Expert/TopicView2.asp?id=4498174&datebasetype=now Option Explicit

'VBS 实现求 1000! 位数

'作者: xiaoyuehen(萧月痕)

'日期: 2006-1-6

'MSN: xiaoyuehen(at)msn.com

'大数加法

'参数 x: 加数, y: 被加数

'以数组存储

function GetAddResult(x, y)

Dim arrR(), strX, strY, lx, ly

strX = StrReverse(x)

strY = StrReverse(y)

lx = Len(strX)

ly = Len(strY)

'Msgbox lx

Dim i, iMax, iJinWei

If lx > ly Then

iMax = lx

Else

iMax = ly

End If

ReDim arrR(iMax)

iJinWei = 0

For i = 1 to iMax

arrR(i) = int("0" & Mid(strX, i, 1)) + int("0" & Mid(strY, i, 1)) + iJinWei

iJinWei = arrR(i) \ 10

arrR(i) = Right(arrR(i), 1)

Next

Dim strResult

strResult = StrReverse(Join(arrR, ""))

If Left(strResult, 1) = "0" Or iJinWei = 1 Then

strResult = "1" & strResult

End If

GetAddResult = strResult

End function

'加法

'参数 x: 加数, y: 被加数

'以字符串构造

'该方法经过试验不可行..速度太慢!

function GetAddNResult(x, y)

Dim strX, strY, lx, ly

strX = StrReverse(x)

strY = StrReverse(y)

lx = Len(strX)

ly = Len(strY)

Dim i, iMax, iJinWei

If lx > ly Then

iMax = lx

Else

iMax = ly

End If

Dim iTemp, strResult

iJinWei = 0

iTemp = 0

For i = 1 to iMax

iTemp = int("0" & Mid(strX, i, 1)) + int("0" & Mid(strY, i, 1)) + iJinWei

iJinWei = iTemp \ 10

strResult = (iTemp Mod 10) & strResult

Next

If Left(strResult, 1) = "0" Or iJinWei = 1 Then

strResult = "1" & strResult

End If

GetAddNResult = strResult

End function

'乘法

'参数 x: 大数, y: 小数(一位)

function GetMulResult(x, y)

GetMulResult = 0

Dim i

For i = 1 to y

GetMulResult = GetAddResult(GetMulResult, x)

Next

End function

'乘法

'参数 x: 大数, y: 小数

function GetMultResult(x, y)

GetMultResult = 0

Dim str, lx, ly, i

ly = Len(y)

For i = 1 to ly

GetMultResult = GetAddResult(GetMultResult, GetMulResult(x, CInt(Mid(y, i, 1))) & String(ly - i, "0"))

Next

End function

'乘法

'参数 x: 大数, y: 大数

function GetMulcResult(x, y)

If Len(x) > Len(y) Then

GetMulcResult = GetMultResult(x, y)

Else

GetMulcResult = GetMultResult(y, x)

End If

End function

'阶乘

'参数 x: 自然数

function GetFactorialResult(x)

GetFactorialResult = x

Dim i

For i = (x - 1) to 2 step - 1

GetFactorialResult = GetMulcResult(GetFactorialResult, i)

Next

End function

'直接求阶乘位数

'参数 x: 自然数

'原作: aiur2000(闭关失败,走火入魔,开关拉!)

'vbs代码实现: xiaoyuehen

function GetFactorialLength(x)

Dim iLen, iSum, iVal, i

'思路:因为不计算具体值,所以没必要全部算出,只用计算能影响到结果的位数即可,同时要加入下次影响结果的值.

'做法:每次的积取下次乘数的位数的2倍即可.

'下一个乘数的位数

iLen = 0

'位数

iSum = 0

'积

iVal = 1

For i = 1 to x

iLen = Len(i)

'如果积超过乘数位数2倍,后面的记入汇总位数

If Len(iVal) > iLen * 2 Then

iSum = iSum + (Len(iVal) - iLen * 2)

iVal = Left(iVal, iLen * 2)

End If

iVal = iVal * i

Next

GetFactorialLength = Len(iVal) + iSum

End function

'下面开始各项测试

Dim t, x, y

t = Timer

x = String(1000, "9")

y = String(1000, "9")

'y = String(200, "9")

'Msgbox " String 总用时: " & FormatNumber(Timer - t) & " 秒"

't = Timer

'Call GetAddResult(x, y)

'Msgbox " GetAddResult: " & "GetAddResult(x, y)" & " 总用时: " & FormatNumber(Timer - t) & " 秒"

t = Timer

'Call GetFactorialLength(1000)

Msgbox " GetFactorialLength(1000): " & GetFactorialLength(1000) & " 总用时: " & FormatNumber(Timer - t) & " 秒"

't = Timer

'Call GetMulResult(x, y)

'Msgbox " GetMulResult: " & GetMulResult(x, y) & " 总用时: " & FormatNumber(Timer - t) & " 秒"

't = Timer

'Call GetMulResult(x, y)

'Msgbox " GetMultResult: " & GetMultResult(x, y) & " 总用时: " & FormatNumber(Timer - t) & " 秒"

't = Timer

'Call GetMulResult(x, y)

'Msgbox " GetMulcResult: " & GetMulcResult(x, y) & " 总用时: " & FormatNumber(Timer - t) & " 秒"

't = Timer

'Call GetAddResult(x, y)

'Msgbox " GetAddResult 总用时: " & FormatNumber(Timer - t) & " 秒"

't = Timer

'Call GetAddNResult(x, y)

'Msgbox " GetAddNResult 总用时: " & FormatNumber(Timer - t) & " 秒"

'x = 300

't = Timer

'Call GetFactorialResult(x)

'Msgbox " GetFactorialResult(" & x & ") = " & GetFactorialResult(x) & " 总用时: " & FormatNumber(Timer - t) & " 秒"

'Msgbox " 共 " & Len(GetFactorialResult(x)) & " 位, 用时: " & FormatNumber(Timer - t) & " 秒"

 
 
 
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