Given that val is some random integer,
and number the possible outcome:
if the value is less then &H100 ; the number is 0
if the value is less then &H10000 ; the number is 1
if the value is less then &H1000000 ; the number is 2
else ; the number is 3
I've got this:
If (val And &HFFFF0000) = 0 Then
If (val And &HFF00) = 0 Then
num = 0
Else
numb = 1
End If
ElseIf (**val** And &HFF000000) = 0 Then
numb = 2
Else
numb = 3
End If
I believe to remember that I could achieve this with a simple calculation, but I can not
wrap my head around it...
cheers..
Jhonny
edit:--- after reaction of video.baba ---
Here is half a solution:
The result is a number from 0 to 7, of witch the bits represent a non-zero byte.
A lookuptable could be used to translate it to a 2-bit value.
val >>= 8 ' move to the right, so the first byte can hold identification-bits
val += &H3FF0000 'set a bit in the first byte, if the second one is not zero
val = val And &H400FFFF
val += &H1FFFF00 'set a bit in the first byte, if the third one is not zero
val = val And &H60000FF
val += &HFFFFFF'set a bit in the first byte, if the fourth one is not zero
val >>= 24 'put the result in the last byte
number=lookuptable(val)
have not tested it for speed yet, but it feels over-complicated?
Do you mean something like:
Select Case Value
Case < &H100
Number = 0
Case < &H10000
Number = 1
Case < &H1000000
Number = 2
Case Else
Number = 3
End Select
Related
In the following project euler program #56, Considering natural numbers of the form, a^b, where a, b < 100, what is the maximum digital sum?
so I wrote the following code:
Dim num As System.Numerics.BigInteger
Dim s As String
Dim sum As Integer
Dim record As Integer
For a = 2 To 99
For b = 1 To 99
num = a ^ b
s = num.ToString
For i = 0 To s.Length - 1
sum += CInt(s.Substring(i, 1))
Next
sum = 0
Next
Next
The answer I got from the program was not the correct answer, so I wrote the following code so I can see what numbers set a new high value and see if something is wrong.
If sum > record Then
record = sum
Console.WriteLine(a & "," & b)
End If
One of the answers was a=10 b= 81. Obviously that doesn't make sense, because that value is 1 + 81 "0" = 1, but watching the result of 10^81, was 999999999999999921281879895665782741935503249059183851809998224123064148429897728
I searched about the accuracy of BigInteger but couldn't find anything, is there something that I'm missing?
Function convertToText(ByVal data As String) As String
Dim result As String = Nothing
Dim i As Integer = 0
Dim j As Integer = 0
For Each c As Char In data.ToCharArray
j *= 2
If c = "1"c Then j += 1
i += 1
If i = 8 Then
i = 0
result &= Chr(j)
j = 0
End If
Next
Return result
End Function
It converts binary to text but its a bit difficult for me to understand the logic behind it.
Someone please help.
The code seems to convert a text containing a binary number representing 8 bit character codes to a string containing these characters.
The for each loop loops over all binary digits ("0" or "1") of the input. The code of each result character is computed and after every 8 input characters the code is considered to be complete and the new character whose code was determined is added to the result (result &= Chr(j) is the same as result = result & Chr(j). Chr(j) converts an Integer containing a character code into a character). The variable i counts the bits.
The variable j holds the character code. If a bit is "1", then 1 is added to j (j += 1 is the same as j = j + 1), but not if it is "0".
A "1" in the right most bit position has a (decimal) value of 1. The next to its left a value of 2. The next 4 and so on. The value doubles for each position until it reaches 128 for the left most bit of an 8 bit number. Therefore j is doubled on each loop (j *= 2 is the same as j = j * 2).
Example with just 4 bits:
data = "1010"
The binary number 1010 means
1 * 8 + 0 * 4 + 1 * 2 + 0 * 1 = (decimal)10
The code does this
j = 0 => 0
j *= 2 => 0
j += 1 => 1 'since c = "1"
j *= 2 => 2
'no += 1 since c = "0"
j *= 2 => 4
j += 1 => 5 'since c = "1"
j *= 2 => 10
'no += 1 since c = "0"
The first 1 we added is doubled 3 times and becomes 8. The second 1 we added is doubled only once and becomes 2. 8 + 2 = 10.
Sorry for the terrible title, but I have no clue on how to generalize (or simplify) my loop case here.
I have a program that iterates to a sequence of integer, for example dimension=1 to 5.
In each iteration, there will be a main loop, and inside the main loop, there will be a nested loop. The number of the nested loop will be [dimension].
For example, in dimension=1, there is a For loop. In dimension=2, there is a For loop inside a For loop. And so on.
Is there any possible way to simplify the algorithm? currently I'm manually write totally different code for each value of [dimension]. Imagine if dimension=1 to 100? I'll be dead.
Here's my piece of program (written in VB.NET)
for dimension=2
Dim result(2) As Integer
For i = 0 To 1
For j = 0 To 1
result(0)=i
result(1)=j
Next
Next
For dimension=3
Dim result(3) As Integer
For i = 0 To 1
For j = 0 To 1
For k = 0 To 1
result(0)=i
result(1)=j
result(2)=k
Next
Next
Next
For dimension=4
Dim result(4) As Integer
For i = 0 To 1
For j = 0 To 1
For k = 0 To 1
For l = 0 To 1
result(0)=i
result(1)=j
result(2)=k
result(3)=l
Next
Next
Next
Next
And so on..
Any suggestion?
Thanks!
There are plenty of solutions:
Recursion
Idk, if vb.net supports methods, but if it does, this would probably be the simplest:
void nestedLoop(int lower , int upper , int remaining_loops , int[] values)
if(remaining_loops == 0)
//process values list
else
for int i in [lower , upper)
values[remaining_loops] = i
nestedLoop(lower , upper , remaining_loops - 1)
Integer Transformation
In theory, a number can be represented by any radix:
d_i * radix ^ i + d_i-1 * radix ^ (i - 1) ... + d_0 * radix ^ 0
Consider each digit the value of one of the nested loops:
for int i in [0 , max)
for int j in [0 , max)
for int k in [0 , max)
...
Could be represented by a 3-digit number with radix max, where d_0 = i, d_1 = j, etc.. Basically how each digit is mapped to one of the values can be arbitrary and will only affect the order of the output.
void nestedLoops(int upper , int dimension)
for int i in [0 , pow(upper , dimension))
int[] values
int digit_sub = 1
int tmp = i
for int j in [0 , dimension)
values[j] = tmp % dimension
tmp /= dimension
//all values of the loops are now in values
//process them here
There would be a few other options aswell, but these are the most common.
Please do note that when you do
Dim result(2) As Integer
You are actually declaring an array of 3 elements see this question for why. It's a subtle difference in VB.NET
That being said, I'll assume that you meant to declare an array of only 2 elements. If this is the case then you could build and call a recursive function like this
LoopOver(result)
Sub LoopOver(ByRef array() As Integer, ByVal Optional level As Integer = 0)
If array.Length = level Then
Return
Else
array(level) = 1
LoopOver(array, level + 1)
End If
End Sub
This recursive function will call itself (i.e., it will loop) for as many times as the array's size.
So my professor gave me a challenge to build a decoder that could break his special formula. It was described to be 32 characters in length, alphanumeric numeric when entered but then "it has a system... the first 106 bits must be 50% 1's and the rest 0's, the remaining 22 bits are basically a hash of the previous bits so that the key can be checked..." were his exact words. Sounds to me like a 128 bit encryption with a twist. I found the below but I need VB2010 or VS2010, this says php.
<?php
function string_random($characters, $length)
{
$string = '';
for ($max = mb_strlen($characters) - 1, $i = 0; $i < $length; ++ $i)
{
$string .= mb_substr($characters, mt_rand(0, $max), 1);
}
return $string;
}
// 128 bits is 16 bytes; 2 hex digits to represent each byte
$random_128_bit_hex = string_random('0123456789abcdef', 32);
// $random_128_bit_hex might be: '4374e7bb02ae5d5bc6d0d85af78aa2ce'
Would that work? Or does it need converting? Please help. Oh and thank you :)
I wasn't promised extra credit but either way I would like to surprise him.
So the first 106 bit are 26 character and the first half of the 27.
You have first of all encode somehow the number of 0 and 1, while building the string you need to keep an eye to the number. An idea would be to build a map like this:
0 = 0000 = -4
1 = 0001 = -2
2 = 0010 = -2
3 = 0011 = 0
4 = -2
5 = 0
6 = 0
7 = +2
8 = -2
9 = 0
a = 0
b = +2
c = 0
d = +2
e = +2
f = +4
then everytime you extract a new random number you check the number associated to it and add it to a variable
balanceOfOneAndZero
your objective is have balanceOfOneAndZero = 0 when you hit your 27th character.
to do that you need a control function, that takes current balanceOfOneAndZero, the proposed character proposedChar, and current string lenght currLenght.
Would be better to split the problem into two part. First is reaching the 26th character of the sequence with balanceOfOneAndZero between -2 and 2. Any other value is not acceptable, because your 27th character can have maximum two 1 or two 0 to completely balance the first 106 characters.
so your function should do something like (I'll write in sort of pseudo code since I don't have an IDE right now)
function checkNextLetter(Dim balanceOfOneAndZero As Integer, Dim proposedChar As Char,
Dim currentLenght as Integer) As Boolean
If( ((26 - currentLenght - 1) * 4 + 2) < MOD(Map.ValueOf(proposedChar) + balanceOfOneAndZero) ) Then
Return true
Else
Return false
ENd If
End function
This function basically check if accepting the new character will still make possible to Balance the number of 0 and 1 before the 26th character.
So your main function should have a loop every time it propose a new character, something like
proposedChar = new RandomChar
While (Not checkNextLetter(balanceOfOneAndZero, proposedChar, len(currentString))
proposedChar = new RandomChar
End While
currentString = currentString & proposedChar
this only until you hit the 26th character.
Than you have to check balanceOfOneAndZero, if its 2 you add a character that begin with 00, if it's 0 you can either have 10 or 01, if it's -2 you have to add a character that begin with 11.
After this I can't help you about the rest 22 character, since there are not enough information. You could brute force the rest
EDIT:
so to brute force the rest (il start from when you reach the 26th character):
Dim stringa1, stringa2, stringa3, stringa4 As String
If balanceOfOneAndZero = 2 Then
stringa1 = currentString & '0'
stringa2 = currentString & '1'
stringa3 = currentString & '2'
stringa4 = currentString & '3'
ELse If balanceOfOneAndZero = 0 Then
stringa1 = currentString & '4'
stringa2 = currentString & '5'
stringa3 = currentString & '6'
stringa4 = currentString & '7'
Else
stringa1 = currentString & 'c'
stringa2 = currentString & 'd'
stringa3 = currentString & 'e'
stringa4 = currentString & 'f'
End if
Function GenerateAllCombination(ByVal iLenght As Integer)
Dim arrayLista As New List(Of String)()
Dim arraySubLista As New List(Of String)()
If (iLenght > 1) Then
arraySubLista = GenerateAllCombination(iLenght -1)
for each objString As String in arraySubLista
for each ele As String in arrayValori
arrayLista.add(objString & ele)
loop
loop
Else
for each ele As String in arrayValori
arrayLista.add(ele)
loop
End If
End Function
Now if you use generateAllCombination you will have a List of string with ALL the combination of 5 character.
Now you just create 4 list by concatenating those combination with your string1 to string4 (string1 & combination) etc..
put all those result on a List of string, and you have 100% that at least ONE of the string will break your teacher code
I forgot, arrayValori must be a List with all values from "0" to "f"
So I'm developing a minesweeper game and im assigning the mines, but I've got to check where are the mines now, in order to generate the numbers. The problem is that when I'm verifying the columns and lines I need the program not to get out of the game field.
Here's how my code looks like now:
Public Sub avisinhos(ByVal line, ByVal column)
If mat(line, column) = 0 Then
mat(line, column) = -1
numbandeiras = numbandeiras + 1
End If
For auxlinha = -1 To 1
For auxcolumn = -1 To 1
Next
Next
End Sub
How do I create a IF function to verify that I don't get out of the game field?
Best regards, joao.
pseudo code
int linestart = -1;
int lineend = 1;
int colstart = -1;
int colend = 1;
Assuming a 10 x 10 grid (zero based)
if line < 2 linestart = 0
if line > 8 lineend = 0
if column < 2 colstart = 0
if column > 8 colend = 0
For auxlinha = linestart To lineend
For auxcolumn = colstart To colend
// check
Next
Next
Personally though I wouldn't bother with the loops, they add very little to nothing
HasMineAbove = (line > 1) and (gamefield[line -1,column] = MinePresentValue
would be my approach, do it all in one.
Not to mention the huge potential confusion when auxlinha and auxcolumn are both zero...
I'm not sure exactly what your code is saying. It's a bit cryptic since you're using abbreviations and all lowercase names. You might want to try camelCasing and spelling out the words more completely, intellisense is your friend. =)
But coding style aside, if you are trying to loop through a limited range of values, you can keep your values bounded by using the modulus operator (%). For example, if you need to keep you values between 0-7 and you end up with a value of 12, just take the modulus of 8 to loop back to within range with a value of 4:
12 % 8 = 4
9 % 8 = 1
15 % 8 = 7
24 % 8 = 0
I realize this doesn't answer your specific question, but it's a handy technique might find useful.