Develop Reference

C# Dynamic programming conversion

Hi I have a task to convert exponential code into linear, but I have no idea how to do it. Could you give me any tips or point me in the right direction?
Here's the code:
int F (int m, int n)
{
if(n == 0)
{
return m;
}
else if(m == 0 && n > 0)
{
return n;
}
else
{
int[] array = { 1 + F(m - 1, n), 1 + F(m, n - 1), D(m, n) + F(m - 1, n - 1) };
return array.Min();
}
}
int D(int i, int f)
{
if(x[i] == y[f])
{
return 1;
}
else
{
return 0;
}
}
Update:
Am I going in the right direction? So far it works only with m=0,1,2 and n=0,1,2. How do I fill all the values if let's say, I give m = 10 and n = 20?
int Fdp(int m, int n)
{
fdin[m, 0] = m;
for(int i = 0; i <= n; i++)
{
fdin[0, i] = n;
}
if (n == 0)
{
return m;
}
else if (m == 0 && n > 0)
{
return n;
}
else
{
int[] temp = { 1 + fdin[m-1, n], 1+ fdin[m,n-1], D(m,n) + fdin[m-1,n-1] };
fdin[m, n] = temp.Min();
return temp.Min();
}
}

Solved it.
static int Fdp(int m, int n)
{
for (int i = 0; i <= m; i++)
{
fdin[i, 0] = i;
for (int j = 1; j <= n; j++)
{
if(i == 0)
{
fdin[i, j] = j;
}
else
{
int[] temp = new int[] { 1 + fdin[i - 1, j], 1 + fdin[i, j - 1], D(i, j) + fdin[i - 1, j - 1] };
fdin[i, j] = temp.Min();
}
}
}
return fdin[m,n];
}

C# how to determine the last iteration of foreach loop

I am trying to build a function that counts the number of zero between ones.
My function is doing just fine for binaries that starts and end with one. But the problem is if the given binary is 100000, it is returning 5. But it should return zero because it is not between ones.
Here is the code.
private static int solution1(int N)
{
string binary = Convert.ToString(N, 2);
int gap = 0;
int longestgap = 0;
foreach (char Z in binary)
{
if (Z == '0') gap++;
if (gap > longestgap) longestgap = gap;
if (Z == '1') gap = 0;
}
return longestgap;
}

All you need to do is move the second if. You dont want to override the longest gap everytime, only if you know it is definitely between two 1's.
if (Z == '0')
{
gap++;
}
else // if (Z == '1')
{
if (gap > longestgap)
{
longestgap = gap;
}
gap = 0;
}
This way, even if the gap keeps counting up until the end of your binary, if you don't find a second '1', the longest gap will still be 0.

Not really tested, but something like this should work:
bool firstOneFound = false; // To account for the case "00001"
foreach (char Z in binary)
{
if (Z == '0')
{
if(firstOneFound)
gap++;
}
else if (Z == '1')
{
if (gap > longestgap)
longestgap = gap;
firstOneFound = true;
gap = 0;
}
}
If you don't need to use a foreach loop, this seems cleaner:
for(int i = binary.IndexOf("1"); i < binary.Length; i++)
{
char Z = binary[i];
if (Z == '0')
{
gap++;
}
else if (Z == '1')
{
if (gap > longestgap)
longestgap = gap;
gap = 0;
}
}

find common substrings in 2 string in c#

I have strings like:
1) Cookie:ystat_tw_ss376223=9_16940400_234398;
2) Cookie:zynga_toolbar_fb_uid=1018132522
3) GET /2009/visuels/Metaboli_120x600_UK.gif HTTP/1.1
4) GET /2010/07/15/ipad-3hk-smv-price-hk/ HTTP/1.1
1 ad 2 have common substtring{cookie:}
3 and 4 have common substtring{GET /20, HTTP/1.1}
I want to find all common substrings that have the length more than three characters(contain space character) between 2 strings.(like 1 and 2)
i want to code in c#. i have a program but it has some problems.
Could anyone help me?
public static string[] MyMCS2(string a, string b)
{
string[] st = new string[100];
// List<string> st = new List<string>();
List<char> f = new List<char>();
int ctr = 0;
char[] str1 = a.ToCharArray();
char[] str2 = b.ToCharArray();
int m = 0;
int n = 0;
while (m < str1.Length)
{
for (n = 0; n < str2.Length; n++)
{
if (m < str1.Length)
{
if (str1[m] == str2[n])
{
if ((m > 1) && (n > 1) &&(str1[m - 1] == str2[n - 1]) && (str1[m - 2] == str2[n - 2]))
{
//f[m]= str1[m];
f.Add(str1[m]);
char[] ff = f.ToArray();
string aaa = new string(ff);
if (aaa.Length >= 3)
{
st[ctr] = aaa + "()";
//st.Add(aaa);
ctr++;
}
kk = m;
m++;
}
else if ((n == 0) ||(n == 1))
{
f.Add(str1[m]);
kk = m;
m++;
}
else
f.Clear();
}
//else if ((str1[m] == str2[n]) && (m == str1.Length - 1) && (n == str2.Length - 1))
//{
// f.Add(str1[m]);
// char[] ff = f.ToArray();
// string aaa = new string(ff);
// if (aaa.Length >= 3)
// {
// st[ctr] = aaa;
// ctr++;
// }
// // m++;
//}
else if ((str1[m] != str2[n]) && (n == (str2.Length - 1)))
{
m++;
}
else if ((m > 1) && (n > 1) && (str1[m] != str2[n]) && (str1[m - 1] == str2[n - 1]) && (str1[m - 2] == str2[n - 2]) && (str1[m - 3] == str2[n - 3]))
{
//
char[] ff = f.ToArray();
string aaa = new string(ff);
if (aaa.Length >= 3)
{
st[ctr] = aaa + "()" ;
//st.Add(aaa);
ctr++;
f.Clear();
}
//f.Clear();
//for (int h = 0; h < ff.Length; h++)
//{
// f[h] = '\0';
//}
}
else if (str1[m] != str2[n])
continue;
}
}
}
//int gb = st.Length;
return st;
}

This is an exact matching problem not a substring. You can solve it with aho-corasick algorithm. Use the first string and compute a finite state machine. Then process the search string. You can extend the aho-corasick algorithm to use a wildcard and search also for substrings. You can try this animated example: http://blog.ivank.net/aho-corasick-algorithm-in-as3.html

How to process an array correctly

Here's the part 1 of my question, if you wanna check the background of this question :
Detecting brackets in input string
Forgive me if the title doesn't match, since I also confused how to name it appropriately to picture my problem. If anyone knows a more appropriate title, feel free to edit.
So, given below code (my own code) :
private const int PARTICLE_EACH_CHAR = 4;
/*ProcessBarLines : string s only contains numbers, b, [, and ]*/
private int ProcessBarLines(Canvas canvas, string s, int lastLineAboveNotation)
{
List<int> bracket = new List<int>();
List<int> other = new List<int>();
int currentCloseNumber = 0;
int currentOpenNumber = 0;
for (int i = 0; i < s.Length; i++)
{
if (s[i] == '[')
{
bracket.Add(i);
currentOpenNumber++;
if (i - 1 > 0 && s[i - 1] != '[')
{
currentOpenNumber = 1;
}
}
else if (s[i] == ']')
{
bracket.Add(i);
currentCloseNumber++;
if (i + 1 >= s.Length || s[i + 1] != ']' || currentOpenNumber == currentCloseNumber)
{
int min = bracket.Count - (currentCloseNumber * 2);
int max = bracket[bracket.Count - 1];
List<int> proc = new List<int>();
int firstIndex = -1;
int lastIndex = -1;
for (int ii = 0; ii < other.Count; ii++)
{
if (other[ii] > min && other[ii] < max)
{
proc.Add(other[ii]);
if (firstIndex == -1)
{
firstIndex = ii;
lastIndex = ii;
}
else
{
lastIndex = ii;
}
}
}
double leftPixel = firstIndex * widthEachChar;
double rightPixel = (lastIndex * widthEachChar) + widthEachChar;
DrawLine(canvas, currentCloseNumber, leftPixel,
rightPixel, lastLineAboveNotation * heightEachChar / PARTICLE_EACH_CHAR);
lastLineAboveNotation += currentCloseNumber - 1;
currentOpenNumber -= currentCloseNumber;
currentCloseNumber = 0;
}
}
else
{
other.Add(i);
}
}
return lastLineAboveNotation + 1;
}
Here's the test cases :
Picture 1 & 2 is the correct answer, and picture 3 is the wrong answer. Picture 3 should have a line, just like inverted from number 2, but, apparently, (if you look closely) the line is drawn on the right, but it should be on the left to be correct (above 0).
I figured, the problem is, I'm quite sure on the "min". Since it doesn't give the correct starting value.
Any idea on this? Feel free to clarify anything. It's used for writing numeric musical scores.
Btw, DrawLine() just meant to draw the line above the numbers, it's not the problem.

Finally! I found it!
private int ProcessBarLines(Canvas canvas, string s, int lastLineAboveNotation)
{
List<int> bracket = new List<int>();
List<int> other = new List<int>();
int currentCloseNumber = 0;
int currentOpenNumber = 0;
int space = 0;
for (int i = 0; i < s.Length; i++)
{
if (s[i] == '[')
{
bracket.Add(i);
currentOpenNumber++;
if (i - 1 > 0 && s[i - 1] != '[')
{
currentOpenNumber = 1;
}
}
else if (s[i] == ']')
{
bracket.Add(i);
currentCloseNumber++;
if (i + 1 >= s.Length || s[i + 1] != ']' || currentOpenNumber == currentCloseNumber)
{
int min = bracket[Math.Max(bracket.Count - ((currentCloseNumber * 2) + space), 0)];
int max = bracket[bracket.Count - 1];
space = max - min - 1;
List<int> proc = new List<int>();
int firstIndex = -1;
int lastIndex = -1;
for (int ii = 0; ii < other.Count; ii++)
{
if (other[ii] > min && other[ii] < max)
{
proc.Add(other[ii]);
other[ii] = -1;
if (firstIndex == -1)
{
firstIndex = ii;
lastIndex = ii;
}
else
{
lastIndex = ii;
}
}
}
double leftPixel = firstIndex * widthEachChar;
double rightPixel = (lastIndex * widthEachChar) + widthEachChar;
DrawLine(canvas, currentCloseNumber, leftPixel,
rightPixel, lastLineAboveNotation * heightEachChar / PARTICLE_EACH_CHAR);
lastLineAboveNotation += 1;
currentOpenNumber -= currentCloseNumber;
currentCloseNumber = 0;
}
}
else
{
other.Add(i);
}
}
return lastLineAboveNotation + 1;
}
If someone got a more efficient code, please let us know!

C# Check for neighbours

I have a function to check neighbors of an array and if that element is equal with 1. X is for each neighbor found and v[l] is the position for each 0. I have a problem with this code each time gives me "Index was outside the bounds of the array" and i don't know what to do else.
public int modificari(int i,int j,int n,int m)
{
int x = 0;
v = new int[n];
l=0;
if (mat[i, j] == 1)
{
if (j++ < m)
{
if (mat[i, j++] == 1)
x++;
else
{
v[l] = i * n + j + 2;
l++;
}
}
if (j++ < m && i++ < n)
{
if (mat[i++, j++] == 1)
x++;
else
{
v[l] = (i + 1) * n + j + 2;
l++;
}
}
if (i++ < n)
{
if (mat[i++, j] == 1)
x++;
else
{
v[l] = (i + 1) * n + j + 1;
l++;
}
}
if (j-- >= 0 && i++ < n)
{
if (mat[i++, j--] == 1)
x++;
else
{
v[l] = (i + 1) * n + j;
l++;
}
}
if (j-- >= 0)
{
if (mat[i, j--] == 1)
x++;
else
{
v[l] = i * n + j;
l++;
}
}
if (j-- >= 0 && i-- >= 0)
{
if (mat[i--, j--] == 1)
x++;
else
{
v[l] = (i - 1) * n + j;
l++;
}
}
if (i-- >= 0)
{
if (mat[i--, j] == 1)
x++;
else
{
v[l] = (i - 1) * n + j + 1;
l++;
}
}
if (j < n && i-- >= 0)
{
if (mat[i--, j++] == 1)
x++;
else
{
v[l] = (i - 1) * n + j + 2;
l++;
}
}
if (x < 2 && x > 3)
return 1;
else
return random();
}
return x;
}

That is a total mess. It is very hard to follow, even for an experienced coder. Use of one letter variable names and inline ++ operators is usually discouraged for the sake of readability.
I've quickly tried to rewrite your function from my best guess of what you're trying to achieve. I'm hoping you can see a different way to approach the problem that suits you better.
NOTE: I did not test this code at all, it probably has compile errors.
public struct Point
{
public int X;
public int Y;
public Point( int x, int y )
{
X = x;
Y = y;
}
}
public class Whatever
{
// ...
// Here is a list of the positions of all the neighbours whose values are
// zero.
List<Point> zeroPositions = new List<Point>();
// ...
public int Modificari(int pointX, int pointY)
{
// Determine dimensions of array.
int height = mat.GetLength(0);
int width = mat.GetLength(1);
// Find the minimum and maximum positions bounded by array size. (So we
// don't try to look at cell (-1, -1) when considering the neighbours of
// cell (0, 0) for instance.
int left = Math.Max( pointX - 1, 0 );
int right = Math.Min( pointX + 1, width );
int top = Math.Max( pointY - 1, 0 );
int bottom = Math.Min( pointY + 1, height );
// This is the number of neighbours whose value is 1.
int oneCount = 0;
zeroPositions.Clear();
for( int y = top; y <= bottom; y++ )
{
for( int x = left; x <= right; x++ )
{
if( mat[x, y] == 1 )
{
oneCount++;
}
else if( mat[x, y] == 0 )
{
zeroPositions.Add( new Point( x, y ) );
}
}
}
return oneCount;
}
//...
}
Also I'd really advise you to try not to do too many things in a function. Try making a different function for getting positions of ones and for returning the number of zeros.