I have a dynamic matrix and I need to to calculate sum of digits in this way:
0 1 2 3 4 5 6
10 11 12 13 14 15 16
20 21 22 23 24 25 26
30 31 32 33 34 35 36
40 41 42 43 44 45 46
50 51 52 53 54 55 56
60 61 62 63 64 65 66
I can't understand in which way I should compare i and j:
long result = 0;
for (int i = 0; i < len; i++)
{
for (int j = 0; j < len; j++)
{
// only works for diagonal
if (i == j) // should use j - 1 or i - 1?
{
result += matrix[i][j];
}
}
}
no need to scan full matrix:
long result = 0;
for (int i = 0; i < len; i++)
{
result += matrix[i][i]; // diagonal
if (i < len - 1) // stay within array bounds
result += matrix[i][i+1]; // next to diagonal
}
modification without index check on every iteration:
// assign corner value from bottom row to result
long result = matrix[len-1][len-1];
// for each row (except last!) add diagonal and next to diagonal values
for (int i = 0; i < len-1; i++)
result += matrix[i][i] + matrix[i][i+1];
Related
Input examples:
7 9 12 16 18 21 25 27 30 34 36 39 43 45 48 52 54 57 61
7 9 12 16 18 21 25 27 30 34 36 39 43 45 48 52 54 57 ... 75 79
Note that it ends with a space.
I want to get 57 in the first case and 75 in the second case as integer. I tried with the following:
Convert.ToInt32(Shorten(sequence).Split(' ').ElementAt(sequence.Length - 2));
The problem is that sequence.Length is not really the right index.
You can use the overload for Split() and pass the RemoveEmptyEntires enum:
string input = "7 9 12 16 18 21 25 27 30 34 36 39 43 45 48 52 54 57 61 ";
var splitInput = input.Split(new char[0], StringSplitOptions.RemoveEmptyEntries);
var inputInt = Convert.ToInt32(splitInput[splitInput.Length - 2]);
// inputInt is 57
Doing it this way allows your last element to actually be what you want.
Fiddle here
Based on maccettura's answer, in C# 8 you can simplify index acces like so
var input = "1 2 3";
var parts = input.Split(' ', StringSplitOptions.RemoveEmptyEntries);
var value = parts.Length >= 2 ? Convert.ToInt32(parts[^2]) : null;
How about something that doesn't use strings at all.
public static int? SplitReverseInt(this string str, int ixFromBack)
{
var inWord = false;
var wEnd = 0;
var found = 0;
for (int i = str.Length - 1; i >= 0; i--)
{
var charr = str[i];
if (char.IsWhiteSpace(charr))
{
// we found the beginning of a word
if (inWord)
{
if (found == ixFromBack)
{
var myInt = 0;
for (int j = i+1; j <= wEnd; j++)
myInt = (myInt * 10 + str[j] - '0');
return myInt;
}
inWord = false;
found++;
}
}
else
{
if (!inWord)
{
wEnd = i;
inWord = true;
}
}
}
// word (number) is at the beginning of the string
if (inWord && found == ixFromBack)
{
var myInt = 0;
for (int j = 0; j <= wEnd; j++)
myInt = (myInt * 10 + str[j] - '0');
return myInt;
}
return null;
}
Performance is about 10 times faster on the example strings.
This only loops from the back, and only fetches one number, it doesnt create substrings or an array of strings we don't need.
Use like this:
var numberFromBack = SplitReverseInt(input, 1);
I want to print numbers on label from 1-to 100
The number's sum must be dividing on 4.
Example:
print 35. because 3+5 = 8 .
8 dividing on 4.
This is code
from loop printing numbers. but how choose those numbers?
print those numbers from 1 to 100 ;
for (int i = 1; i < 100; i++)
{
//select numbers wich sum is dividing on 4
label3.Text += Convert.ToString(i) + " | ";
}
Stolen from Greg Hewgill answer's, you can use his algorithm and use remainder operator (%) like;
int sum, temp;
for (int i = 1; i < 100; i++)
{
sum = 0;
temp = i;
while (temp != 0)
{
sum += temp % 10;
temp /= 10;
}
if (sum % 4 == 0)
{
Console.WriteLine(i);
}
}
Result will be;
4
8
13
17
22
26
31
35
39
40
44
48
53
57
62
66
71
75
79
80
84
88
93
97
Here a demonstration.
You should use a nested loop for that , and use the % operator (% means the rest of division):
for (int i = 1; i < 100; i++)
{
for (int j = i; j < 100; j++)
{
//select numbers wich sum is dividing on 4
if( (i+j)%4 == 0)
{
label3.Text += Convert.ToString(i) + Convert.ToString(j) " | ";
}
}
}
I am trying to make a multiplication table appear on a page based on input from the user. This is my code:
<asp:GridView runat="server" ID="TableData"></asp:GridView>
List<List<int>> nestedList = new List<List<int>>();
protected void LoadTable(int val)
{
for (int y = 0; y <= val; y++)
{
List<int> list = new List<int>();
for (int x = 0; x <= val; x++)
list.Add(x * y);
nestedList.Add(list);
}
TableData.DataSource = nestedList;
TableData.DataBind();
}
But this displays as:
Capacity Count
16 14
16 14
16 14
16 14
16 14
16 14
16 14
16 14
16 14
16 14
16 14
16 14
16 14
16 14
What am I doing wrong?
For clarification, if the user enters 5, the output should be:
0 0 0 0 0 0
0 1 2 3 4 5
0 2 4 6 8 10
0 3 6 9 12 15
0 4 8 12 16 20
0 5 10 15 20 25
I am not worried about column or row headers at this time.
The problem is with your items Source.
a list< list < ?? > > is not a good choice (as i think).
For a Linear view you can use this approach
Code Snippet
var objList = new List<object>();
for (int i = 0; i < 5; i++)
{
var temp = new { operation = string.Format("{0} * {1}", i, i + 1), result = i * (i + 1) };
objList.Add(temp);
}
GridView does not support 2d list binding, consider using another methode.
For exemple, use a simple List , each string will represent a row, you can fill up each string by using a loop that goes like :
(first loop)
{
string s;
for(int x = 0; x < val; x ++)
{
s += (x * y).Tostring() + " ");
}
nestedList.Add(s);
}
I just started learning how to program in c #, so don't shoot me if I have "dumb" questions or questions to which the answer is probably very logical.
I have the next assignment:
Use a for loop to write the next pattern:
1 2 3 4 5 6 7 8 9 10 10
11 12 13 14 15 16 17 18 19 20 20
21 22 23 24 25 26 27 28 29 30 30
31 32 33 34 35 36 37 38 39 40 40
41 42 43 44 45 46 47 48 49 50 50
51 52 53 54 55 56 57 58 59 60 60
61 62 63 64 65 66 67 68 69 70 70
71 72 73 74 75 76 77 78 79 80 80
81 82 83 84 85 86 87 88 89 90 90
91 92 93 94 95 96 97
It has to be possible for the user to set a maximum (in this example 97) and then rerun the application without restarting.
What I am trying now is this:
class Program
{
static void Main(string[] args)
{
string output = "", input = "";
int MaxWaarde, karakters = 15;
do
{
Console.WriteLine("Gelieve het maximum van de matrix in te geven");
input = Console.ReadLine();
MaxWaarde = Convert.ToInt32(input);
for (int i = 1; i <= MaxWaarde; i += 11)
{
Console.Write(i);
for (int j = i; j < MaxWaarde + 1; j += karakters)
{
Console.Write(j);
}
Console.WriteLine(karakters + "");
}
Console.Write("\nOpnieuw een matrix aanmaken? (y/n): ");
output = Console.ReadLine();
}
while (output.ToLower() == "y");
}
}
Which isn't correct at all, but I have been trying to fix this for a while now, and I think I have been staring myself blind at this one, so i really don't know which way to go with this anymore.
Somebody who can give me some advice on how to make this right?
Nested for loops doesn't seem like a good idea here.You can do it with one for loop.You are incrementing i +11 in every step,probably your mistake is here. Consider this:
for (int i = 1; i <= MaxWaarde; i++)
{
if(i % 10 != 0) Console.Write(i + " ");
else
{
Console.Write(i + " " + i + "\n");
}
}
% is modulus operator.We are looking for remainder of currentNumber / 10, if it's not zero we write the number.If it is then we write value twice and adding a newline character with \n to go the next line.Also You can use Console.WriteLine() instead of \n
Loop1: Count up from 1 to number by step 1. If number is a multiple of 10 it writes that number again with line feed.
Loop2: Do loop1 again as long user wishes.
Here you go
public static void Main(string[] args)
{
for (;;)
{
var val = int.Parse(Console.ReadLine());
for (int i = 1; i <= val; i++)
{
if (i % 10 == 0)
{
Console.WriteLine("{0} {0}", i);
}
else
{
Console.Write("{0} ", i);
}
}
Console.WriteLine();
}
}
My math is a bit rusty. I'm trying to equalize a histogram of a 2D array which represents grayscale values in the range 0-255 (values may not be whole numbers because of how they are computed).
I found this article on Wikipedia, but I don't quite understand the formulas they present.
ni, n and L I can compute, but I'm not quite sure how to implement this cdf function. Might this function be of use?
Here's what I've got so far:
static double[,] Normalize(double[,] mat)
{
int width = mat.GetLength(0);
int height = mat.GetLength(1);
int nPixels = width*height;
double sum = 0;
double max = double.MinValue;
double min = double.MaxValue;
var grayLevels = new Dictionary<double, int>();
foreach (var g in mat)
{
sum += g;
if (g > max) max = g;
if (g < min) min = g;
if (!grayLevels.ContainsKey(g)) grayLevels[g] = 0;
++grayLevels[g];
}
double avg = sum/nPixels;
double range = max - min;
var I = new double[width,height];
// how to normalize?
return I;
}
Found something that you might find useful
http://sonabstudios.blogspot.in/2011/01/histogram-equalization-algorithm.html
Hope that helps
Calculating the cumulative distribution function involves a couple of steps.
First you get the frequency distribution of your grayscale values.
So something like:
freqDist = new int[256];
for each (var g in mat)
{
int grayscaleInt = (int)g;
freqDist[grayscaleInt]++;
}
Then to get your CDF, something like:
cdf = new int[256];
int total = 0;
for (int i = 0; i < 256; i++)
{
total += freqDist[i];
cdf[i] = total;
}
I can help you to understand your link,
first, counting value which represent image, shows in that link,
Value Count Value Count Value Count Value Count Value Count
52 1 64 2 72 1 85 2 113 1
55 3 65 3 73 2 87 1 122 1
58 2 66 2 75 1 88 1 126 1
59 3 67 1 76 1 90 1 144 1
60 1 68 5 77 1 94 1 154 1
61 4 69 3 78 1 104 2
62 1 70 4 79 2 106 1
63 2 71 2 83 1 109 1
it is means, the image is created with values above, nothing else.
second, sums the value cumulatively from 52 to 154
Value cdf Value cdf Value cdf Value cdf Value cdf
52 1 64 19 72 40 85 51 113 60
55 4 65 22 73 42 87 52 122 61
58 6 66 24 75 43 88 53 126 62
59 9 67 25 76 44 90 54 144 63
60 10 68 30 77 45 94 55 154 64
61 14 69 33 78 46 104 57
62 15 70 37 79 48 106 58
63 17 71 39 83 49 109 59
it is means,
value 52 have 1 cdf cause it is initial value,
value 55 have 4 cdf cause it has 3 count in image plus 1 cdf from 52,
value 58 have 6 cdf cause it has 2 count in image plus 4 cdf from 55,
and so on.. till..
value 154 have 64 cdf cause it has 1 count in image plus 63 cdf from 144.
then, calculating histogram equalization formula for each image values based on the function
cdf(v) is represent current cdf value from current image value,
in this case, if h(v) = 61 so cdf(v) = 14
cdfmin is represent initial cdf value, in this case, 1 cdf from value 52
happy coding.. ^^
Here's my implementation:
private static byte[,] Normalize(byte[,] mat)
{
int width = mat.GetLength(0);
int height = mat.GetLength(1);
int nPixels = width*height;
var freqDist = new int[256];
foreach (var g in mat)
{
++freqDist[g];
}
var cdf = new int[256];
int total = 0;
for (int i = 0; i < 256; ++i)
{
total += freqDist[i];
cdf[i] = total;
}
int cdfmin = 0;
for (int i = 0; i < 256; ++i)
{
if (cdf[i] > 0)
{
cdfmin = cdf[i];
break;
}
}
var I = new byte[width,height];
double div = (nPixels - cdfmin) / 255d;
for (int y = 0; y < height; ++y)
{
for (int x = 0; x < width; ++x)
{
I[x, y] = (byte)Math.Round((cdf[mat[x, y]] - cdfmin) / div);
}
}
return I;
}
I changed it from using doubles to bytes to work better with the histogram (freqDist).
In addition to what John says, you will need to use the cdf array to compute the new value for every pixel. You do this by:
Adjust John's second iteration to get the first i that has a
freqDist > 0 and call that i imin
Going pixel by pixel i,j between 0 and width and 0 and height repectively and
evaluating round((cdf[pixel[i,j]]-cdf[imin])/(width*height-cdf[imin]))*255),
that is the normalized pixel value at that location.
You can use this function I just wrote:
public static Bitmap ContrastStretch(Bitmap srcImage, double blackPointPercent = 0.02, double whitePointPercent = 0.01)
{
BitmapData srcData = srcImage.LockBits(new Rectangle(0, 0, srcImage.Width, srcImage.Height), ImageLockMode.ReadOnly,
PixelFormat.Format32bppArgb);
Bitmap destImage = new Bitmap(srcImage.Width, srcImage.Height);
BitmapData destData = destImage.LockBits(new Rectangle(0, 0, destImage.Width, destImage.Height),
ImageLockMode.WriteOnly, PixelFormat.Format32bppArgb);
int stride = srcData.Stride;
IntPtr srcScan0 = srcData.Scan0;
IntPtr destScan0 = destData.Scan0;
var freq = new int[256];
unsafe
{
byte* src = (byte*) srcScan0;
for (int y = 0; y < srcImage.Height; ++y)
{
for (int x = 0; x < srcImage.Width; ++x)
{
++freq[src[y*stride + x*4]];
}
}
int numPixels = srcImage.Width*srcImage.Height;
int minI = 0;
var blackPixels = numPixels*blackPointPercent;
int accum = 0;
while (minI < 255)
{
accum += freq[minI];
if (accum > blackPixels) break;
++minI;
}
int maxI = 255;
var whitePixels = numPixels*whitePointPercent;
accum = 0;
while (maxI > 0)
{
accum += freq[maxI];
if (accum > whitePixels) break;
--maxI;
}
double spread = 255d/(maxI - minI);
byte* dst = (byte*) destScan0;
for (int y = 0; y < srcImage.Height; ++y)
{
for (int x = 0; x < srcImage.Width; ++x)
{
int i = y*stride + x*4;
byte val = (byte) Clamp(Math.Round((src[i] - minI)*spread), 0, 255);
dst[i] = val;
dst[i + 1] = val;
dst[i + 2] = val;
dst[i + 3] = 255;
}
}
}
srcImage.UnlockBits(srcData);
destImage.UnlockBits(destData);
return destImage;
}
static double Clamp(double val, double min, double max)
{
return Math.Min(Math.Max(val, min), max);
}
The defaults mean that the darkest 2% of pixels will become black, the lightest 1% will become white, and everything in between will be stretched to fill the color space. This is the same as the default for ImageMagick.
This algorithm has the fun side effect that if you use values above 50% then it will invert the image! Set to .5, .5 to get a black & white image (2 shades) or 1, 1 to get a perfect inversion.
Assumes your image is already grayscale.