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Get Occurrences of Letters in A String

I am trying to count occurrences of letters in a string and almost got the result using the below code snippet:
public static void GetNoofLetters()
{
string str = "AAAAABBCCCDDDD";
int count = 1;
char[] charVal = str.ToCharArray();
List<string> charCnt = new List<string>();
string concat = "";
//Getting each letters using foreach loop
foreach (var ch in charVal)
{
int index = charCnt.FindIndex(c => c.Contains(ch.ToString())); //Checks if there's any existing letter in the list
if(index >= 0) //If letter exists, then count and replace the last value
{
count++;
charCnt[charCnt.Count - 1] = count.ToString() + ch.ToString();
}
else
{
charCnt.Add(ch.ToString()); //If no matching letter exists, then add it to the list initially
count = 1;
}
}
foreach (var item in charCnt)
{
concat += item;
}
Console.WriteLine(concat.Trim());
}
The code works for the given input sample and returns output as: 5A2B3C4D. Simple is that.
But say I've the following input: Second input sample
string str = "AAAAABBCCCDDDDAA";
Expected output:
5A2B3C4D2A
With the above code that I've returns the output as follows:
5A2B3C6A
The above actually occurred for the below code snippet:
if(index >= 0) //If letter found, then count and replace the last value
{
count++;
charCnt[charCnt.Count - 1] = count.ToString() + ch.ToString();
}
Is there any better idea that I can resolve to get the expected output for the second input sample? I can understand, am close enough and may be missing something that's simple enough.
Code sample: Count Occurrences of Letters

Why don't we just loop over value and count? We can have two possibilities:
When character c doesn't equal to current (we have the different character) we should write down the previous sequence and start a new one
Otherwise, add 1 to count
Code:
private static string Compress(string value) {
if (string.IsNullOrEmpty(value))
return value;
char current = '\0';
int count = 0;
StringBuilder result = new StringBuilder(2 * value.Length);
foreach (char c in value) {
if (count != 0 && c != current) {
result.Append(count);
result.Append(current);
count = 0;
}
current = c;
count += 1;
}
result.Append(count);
result.Append(current);
return result.ToString();
}
Please, fiddle yourself

Well, I ended with the following code sample:
public static void Main()
{
string str = "AAAAABBCCCDDDDAABBBBAABB";
int count = 1;
char[] charVal = str.ToCharArray();
List<string> charCnt = new List<string>();
charCnt.Add("");
string concat = "";
//Getting each letters using foreach loop
foreach (var ch in charVal)
{
var lastItem = charCnt.LastOrDefault();
if (lastItem.EndsWith((ch.ToString()))) //If letter exists, then count and replace the last value
{
count++;
charCnt[charCnt.Count - 1] = count.ToString() + ch.ToString();
}
else
{
charCnt.Add(ch.ToString()); //If no matching letter exists, then add it to the list initially
count = 1;
}
}
foreach (var item in charCnt)
{
concat += item; //Concatenate items from the list
}
Console.WriteLine(concat.Trim());
}
Here's a woking sample: Get Occurrences of Letters in A String

How do I make my own String.Split() and Array.Reverse() built-in functions in one user-defined function to reverse a given string?

I have tried this:
using System;
using System.Collections;
using System.Collections.Generic;
public class HelloWorld
{
public static string reverseWords(string str){
ArrayList strArr = new ArrayList();
int start = 0;
string revStr = "";
for(int i = 0; i < str.Length; i++){
if(str[i] == ' '){ // if there's a space,
while(start <= str[i - 1]){ // loop thru the iterated values before space
strArr.Add(str[start]); // add them to the ArrayList
start++; // increment `start` until all iterated values are-
} // stored and also for the next word to loop thru
}
}
for(int j = strArr.Count - 1; j >= 0; j--){
revStr += strArr[j] + " "; // keep appending ArrayList values to the-
} // string from the last to the first value
return revStr;
}
public static void Main(string[] args)
{
Console.WriteLine(reverseWords("Our favorite color is Pink"));
//Expected output : Pink is color favorite Our
}
}
And it's giving this error:
System.IndexOutOfRangeException: Index was outside the bounds of the array.
Please help me understand why this is not working. And also, if there's better way to do this ReverseWord function manually(not using any built-in functions at all).
I'm sorry if this is such a noob question. Any constructive criticism is appreciated. Thanks!

Here is a little improved version of your code that actually works for what you are willing to do.
using System;
using System.Collections;
public class HelloWorld
{
public static string reverseWords(string str){
ArrayList strArr = new ArrayList();
string currentWordString = string.Empty;
string revStr = string.Empty;
for(int i = 0; i < str.Length; i++){
if(str[i] == ' '){ // if there's a space,
strArr.Add(currentWordString); // add the accumulated word to the array
currentWordString = string.Empty; // reset accumulator to be used in next iteration
}else {
currentWordString += str[i]; // accumulate the word
}
}
strArr.Add(currentWordString); // add last word to the array
for(int j = strArr.Count - 1; j >= 0; j--){
revStr += strArr[j] + " "; // keep appending ArrayList values to the-
} // string from the last to the first value
return revStr;
}
public static void Main(string[] args)
{
Console.WriteLine(reverseWords("Our favorite color is Pink"));
//Expected output : Pink is color favorite Our
}
}
I'll let you do the remaining. Like removing the trainling space at the end of the sentence. add seperators other than space (e.g comma, semicolons...)

Try this
"Our favorite color is Pink".Split('\u0020').Reverse().ToList().ForEach(x =>
{
Console.WriteLine(x);
});

This will help
public static string ReverseCharacters(string str)
{
if(str == null)
{
throw new ArgumentNullException(nameof(str));
}
int lastIndex = str.Length - 1;
char[] chars = new char[str.Length];
char temp;
for(int i = 0; i < str.Length/2+1; i++)
{
// Swap. You could refactor this to its own method if needed
temp = str[i];
chars[i] = str[lastIndex - i];
chars[lastIndex - i] = temp;
}
return new string(chars);
}
public static string ReverseWords(string str)
{
if (str == null)
{
throw new ArgumentNullException(nameof(str));
}
if (string.IsNullOrWhiteSpace(str))
{
return str;
}
string space = " ";
StringBuilder reversed = new StringBuilder();
// reverse every characters
var reversedCharacters = ReverseCharacters(str);
// split words (space being word separator here)
var reversedWords = reversedCharacters.Split(space);
// for every revered word characters, reverse it back one more time and append.
foreach(var reversedWord in reversedWords)
{
reversed.Append(ReverseCharacters(reversedWord)).Append(space);
}
// remove last extra space
reversed = reversed.Remove(reversed.Length - 1, 1);
return reversed.ToString();
}
Here is the test result:

Reverse word of full sentence using for loop in c#

I want to print the string in reverse format in for loop:
Input: I'm Learning c#
Output: c# Learning I'm
No Split functions and reverse functions should be used, it has to do only with forloop.
for (int i = m.Length - 1; i >= 0; i--)
{
b[j]=a[i];
j++;
if(a[i]==' '|| a[i]==0)
{
for (int x = b.Length - 1; x >= 0; x--)
{
c[k] = b[x];
Console.Write(c[k]);
k++;
}
}
} Console.ReadKey();

You have to create an array of the words in the sentence:
var words = input.Split(' ');
Then you just loop through the above array from the end to the start:
for(int i=words.Length-1; i>=0; i--)
{
Console.Write(words[i]+" ");
}

With LINQ and string methods you can simplify it:
var reversedWords = input.Split().Reverse(); // Split without parameters will use space, tab and new-line characters as delimiter
string output = string.Join(" ", reversedWords); // build reversed words, space is delimiter

Use Stack<Queue<char>>
Hey if you want to show off your knowledge of data structures, use a queue and a stack! This makes for a very concise answer as well.
You want the sentence to be LIFO with respect to words but FIFO with respect to letters within words, so you need a stack (which are LIFO) of queues (which are FIFO). You can take advantage of the fact that a string, a queue<char>, and a stack<char> all expose IEnumerable<char> as well, so it's easy to convert back and forth; once you have all the characters ordered in your data structure, you can extract the whole thing as a character array using SelectMany(), which you can pass to a string constructor for the final answer.
This solution uses no Split() or Reverse() functions, as required.
public static string ReverseSentence(string input)
{
var word = new Queue<char>();
var sentence = new Stack<IEnumerable<char>>( new [] { word } );
foreach ( char c in input )
{
if (c == ' ')
{
sentence.Push( " " );
sentence.Push( word = new Queue<char>() );
}
else
{
word.Enqueue(c);
}
}
return new string( sentence.SelectMany( w => w ).ToArray() );
}
Usage:
public void Test()
{
var input = "I'm Learning c#";
var output = ReverseSentence(input);
Console.WriteLine(output);
}
Output:
c# Learning I'm
DotNetFiddle

Without split and reverse, I modify your logic little bit to achieve what you need
namespace MyNamespace
{
public class Program
{
public static void Main(string[] args)
{
var m="this is mystring";
var b = new char [m.Length];
var j=0;
//Your code goes here
for (int i = m.Length - 1; i >= 0; i--)
{
b[j]=m[i];
j++;
if(m[i]==' ' || i==0)
{
if(i==0)
{
b[j]=' ';
}
for (int x = b.Length - 1; x >= 0; x--)
{
Console.Write(b[x]);
}
b=new char[m.Length];
j=0;
}
}
Console.ReadKey();
Console.WriteLine("Hello, world!");
}
}
}
Input: "this is mystring"
Output: "mystring is this"

Here is a simple console application for your question
Without using Reverse and Split methods (just for loop)
class Program
{
static void Main()
{
string input = "I'm learning C#";
string[] result = new string[3];
int arrayIndex = 0;
string tempStr = "";
// Split string
for (int i = 0; i < input.Length; i++)
{
tempStr += input[i].ToString();
if (input[i] != ' ')
{
result[arrayIndex] = tempStr;
}
else
{
tempStr = "";
arrayIndex++;
}
}
// Display Result
for (int i = result.Length - 1; i >= 0; i--)
{
System.Console.Write(result[i] + ' ');
}
System.Console.WriteLine();
}
}
Press Ctrl + F5 to run the program
Output: C# learning I'm

How to reverse an array of strings without changing the position of special characters in C#

I'm working on reversing a sentence. I'm able to do it. But I'm not sure, how to reverse the word without changing the special characters positions. I'm using regex but as soon as it finds the special characters it's stopping the reversal of the word.
Following is the code:
Console.WriteLine("Enter:");
string w = Console.ReadLine();
string rw = String.Empty;
String[] arr = w.Split(' ');
var regexItem = new Regex("^[a-zA-Z0-9]*$");
StringBuilder appendString = new StringBuilder();
for (int i = 0; i < arr.Length; i++)
{
char[] chararray = arr[i].ToCharArray();
for (int j = chararray.Length - 1; j >= 0; j--)
{
if (regexItem.IsMatch(rw))
{
rw = appendString.Append(chararray[j]).ToString();
}
}
sb.Append(' ');
}
Console.WriteLine(rw);
Console.ReadLine();
Example : Input
Marshall! Hello.
Expected output
llahsram! olleh.

A basic solution with regex and LINQ. Try it online.
public static void Main()
{
Console.WriteLine("Marshall! Hello.");
Console.WriteLine(Reverse("Marshall! Hello."));
}
public static string Reverse(string source)
{
// we split by groups to keep delimiters
var parts = Regex.Split(source, #"([^a-zA-Z0-9])");
// if we got a group of valid characters
var results = parts.Select(x => x.All(char.IsLetterOrDigit)
// we reverse it
? new string(x.Reverse().ToArray())
// or we keep the delimiters as it
: x);
// then we concat all of them
return string.Concat(results);
}
The same solution without LINQ. Try it online.
public static void Main()
{
Console.WriteLine("Marshall! Hello.");
Console.WriteLine(Reverse("Marshall! Hello."));
}
public static bool IsLettersOrDigits(string s)
{
foreach (var c in s)
{
if (!char.IsLetterOrDigit(c))
{
return false;
}
}
return true;
}
public static string Reverse(char[] s)
{
Array.Reverse(s);
return new string(s);
}
public static string Reverse(string source)
{
var parts = Regex.Split(source, #"([^a-zA-Z0-9])");
var results = new List<string>();
foreach(var x in parts)
{
results.Add(IsLettersOrDigits(x)
? Reverse(x.ToCharArray())
: x);
}
return string.Concat(results);
}

This is a solution without LINQ. I wasn't sure about what are considered special characters.
string sentence = "Marshall! Hello.";
List<string> words = sentence.Split(' ').ToList();
List<string> reversedWords = new List<string>();
foreach (string word in words)
{
char[] arr = new char[word.Length];
for( int i=0; i<word.Length; i++)
{
if(!Char.IsLetterOrDigit((word[i])))
{
for ( int x=0; x< i; x++)
{
arr[x] = arr[x + 1];
}
arr[i] = word[i];
}
else
{
arr[word.Length - 1 - i] = word[i];
}
}
reversedWords.Add(new string(arr));
}
string reversedSentence = string.Join(" ", reversedWords);
Console.WriteLine(reversedSentence);
And this is the output:
Updated Output = llahsraM! olleH.

Here is a non-regex version that does what you want:
var sentence = "Hello, john!";
var parts = sentence.Split(' ');
var reversed = new StringBuilder();
var charPositions = sentence.Select((c, idx) => new { Char = c, Index = idx })
.Where(_ => !char.IsLetterOrDigit(_.Char));
for (int i = 0; i < parts.Length; i++)
{
var chars = parts[i].ToCharArray();
for (int j = chars.Length - 1; j >= 0; j--)
{
if (char.IsLetterOrDigit(chars[j]))
{
reversed.Append(chars[j]);
}
}
}
foreach (var ch in charPositions)
{
reversed.Insert(ch.Index, ch.Char);
}
// olleH, nhoj!
Console.WriteLine(reversed.ToString());
Basically the trick is to remember the position of special (i.e. non letter or digit) characters and insert them at the end to those positions.

This solution is without LINQ and Regex. It may not be an efficient answer but working properly for small string values.
// This will reverse the string and special characters will just stay there.
public string ReverseString(string rString)
{
StringBuilder ss = new StringBuilder(rString);
int y = 0;
// The idea is to swap values. Like swapping first value with last one. It will keep swapping unless it reaches at the middle of the string where no swapping will be needed.
// This first loop is to detect first values.
for(int i=rString.Length-1;i>=0;i--)
{
// This condition is to check if the values is String or not. If it is not string then it is considered as special character which will just stay there at same old position.
if(Char.IsLetter(Convert.ToChar(rString.Substring(i,1))))
{
// This is second loop which is starting from end to swap values from end with first.
for (int k = y; k < rString.Length; k++)
{
// Again checking last values if values are string or not.
if (Char.IsLetter(Convert.ToChar(rString.Substring(k, 1))))
{
// This is swapping. So st1 is First value in that string
// st2 is the last item in that string
char st1 = Convert.ToChar(rString.Substring(k, 1));
char st2 = Convert.ToChar(rString.Substring(i, 1));
//This is swapping. So last item will go to first position and first item will go to last position, To make sure string is reversed.
// Remember when the string value is Special Character, swapping will move forward without swapping.
ss[rString.IndexOf(rString.Substring(i, 1))] = st1;
ss[rString.IndexOf(rString.Substring(k, 1))] = st2;
y++;
// When the swapping is done for first 2 items. The loop will stop to change the values.
break;
}
else
{
// This is just increment if value was Special character.
y++;
}
}
}
}
return ss.ToString();
}
Thanks!

split a string with max character limit

I'm attempting to split a string into many strings (List) with each one having a maximum limit of characters. So say if I had a string of 500 characters, and I want each string to have a max of 75, there would be 7 strings, and the last one would not have a full 75.
I've tried some of the examples I have found on stackoverflow, but they 'truncate' the results. Any ideas?

You can write your own extension method to do something like that
static class StringExtensions
{
public static IEnumerable<string> SplitOnLength(this string input, int length)
{
int index = 0;
while (index < input.Length)
{
if (index + length < input.Length)
yield return input.Substring(index, length);
else
yield return input.Substring(index);
index += length;
}
}
}
And then you could call it like this
string temp = new string('#', 500);
string[] array = temp.SplitOnLength(75).ToArray();
foreach (string x in array)
Console.WriteLine(x);

I think this is a little cleaner than the other answers:
public static IEnumerable<string> SplitByLength(string s, int length)
{
while (s.Length > length)
{
yield return s.Substring(0, length);
s = s.Substring(length);
}
if (s.Length > 0) yield return s;
}

I would tackle this with a loop using C# String.Substring method.
Note that this isn't exact code, but you get the idea.
var myString = "hello world";
List<string> list = new List();
int maxSize
while(index < myString.Length())
{
if(index + maxSize > myString.Length())
{
// handle last case
list.Add(myString.Substring(index));
break;
}
else
{
list.Add(myString.Substring(index,maxSize));
index+= maxSize;
}
}

When you say split, are you referring to the split function? If not, something like this will work:
List<string> list = new List<string>();
string s = "";
int num = 75;
while (s.Length > 0)
{
list.Add(s.Substring(0, num));
s = s.Remove(0, num);
}

i am assuming maybe a delimiter - like space character.
search on the string (instr) until you find the next position of the delimiter.
if that is < your substring length (75) then append to the current substring.
if not, start a new substring.
special case - if there is no delimiter in the entire substring - then you need to define what happens - like add a '-' then continue.

public static string SplitByLength(string s, int length)
{
ArrayList sArrReturn = new ArrayList();
String[] sArr = s.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
foreach (string sconcat in sArr)
{
if (((String.Join(" ", sArrReturn.ToArray()).Length + sconcat.Length)+1) < length)
sArrReturn.Add(sconcat);
else
break;
}
return String.Join(" ", sArrReturn.ToArray());
}
public static string SplitByLengthOld(string s, int length)
{
try
{
string sret = string.Empty;
String[] sArr = s.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
foreach (string sconcat in sArr)
{
if ((sret.Length + sconcat.Length + 1) < length)
sret = string.Format("{0}{1}{2}", sret, string.IsNullOrEmpty(sret) ? string.Empty : " ", sconcat);
}
return sret;
}
catch
{
return string.Empty;
}
}