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Take only letters from the string and reverse them

I'm preparing for my interview, faced the problem with the task. The case is that we're having a string:
test12pop90java989python
I need to return new string where words will be reversed and numbers will stay in the same place:
test12pop90java989python ==> tset12pop90avaj989nohtyp
What I started with:
Transferring string to char array
Use for loop + Char.IsNumber
??
var charArray = test.ToCharArray();
for (int i = 0; i < charArray.Length; i++)
{
if (!Char.IsNumber(charArray[i]))
{
....
}
}
but currently I'm stuck and don't know how to proceed, any tips how it can be done?

You can't reverse a run of letters until you've observed the entire run; until then, you need to keep track of the pending letters to be reversed and appended to the final output upon encountering a number or the end of the string. By storing these pending characters in a Stack<> they are naturally returned in the reverse order they were added.
static string Transform(string input)
{
StringBuilder outputBuilder = new StringBuilder(input.Length);
Stack<char> pending = new Stack<char>();
foreach (char c in input)
if (char.IsNumber(c))
{
// In the reverse order of which they were added, consume
// and append pending characters as long as they are available
while (pending.Count > 0)
outputBuilder.Append(pending.Pop());
// Alternatively...
//foreach (char p in pending)
// outputBuilder.Append(p);
//pending.Clear();
outputBuilder.Append(c);
}
else
pending.Push(c);
// Handle pending characters when input does not end with a number
while (pending.Count > 0)
outputBuilder.Append(pending.Pop());
return outputBuilder.ToString();
}
A similar but buffer-free way is to do it is to store the index of the start of the current run of letters, then walk back through and append each character when a number is found...
static string Transform(string input)
{
StringBuilder outputBuilder = new StringBuilder(input.Length);
int lettersStartIndex = -1;
for (int i = 0; i < input.Length; i++)
{
char c = input[i];
if (char.IsNumber(c))
{
if (lettersStartIndex >= 0)
{
// Iterate backwards from the previous character to the start of the run
for (int j = i - 1; j >= lettersStartIndex; j--)
outputBuilder.Append(input[j]);
lettersStartIndex = -1;
}
outputBuilder.Append(c);
}
else if (lettersStartIndex < 0)
lettersStartIndex = i;
}
// Handle remaining characters when input does not end with a number
if (lettersStartIndex >= 0)
for (int j = input.Length - 1; j >= lettersStartIndex; j--)
outputBuilder.Append(input[j]);
return outputBuilder.ToString();
}
For both implementations, calling Transform() with...
string[] inputs = new string[] {
"test12pop90java989python",
"123test12pop90java989python321",
"This text contains no numbers",
"1a2b3c"
};
for (int i = 0; i < inputs.Length; i++)
{
string input = inputs[i];
string output = Transform(input);
Console.WriteLine($" Input[{i}]: \"{input }\"");
Console.WriteLine($"Output[{i}]: \"{output}\"");
Console.WriteLine();
}
...produces this output...
Input[0]: "test12pop90java989python"
Output[0]: "tset12pop90avaj989nohtyp"
Input[1]: "123test12pop90java989python321"
Output[1]: "123tset12pop90avaj989nohtyp321"
Input[2]: "This text contains no numbers"
Output[2]: "srebmun on sniatnoc txet sihT"
Input[3]: "1a2b3c"
Output[3]: "1a2b3c"

A possible solution using Regex and Linq:
using System;
using System.Text.RegularExpressions;
using System.Linq;
public class Program
{
public static void Main()
{
var result = "";
var matchList = Regex.Matches("test12pop90java989python", "([a-zA-Z]*)(\\d*)");
var list = matchList.Cast<Match>().SelectMany(o =>o.Groups.Cast<Capture>().Skip(1).Select(c => c.Value));
foreach (var el in list)
{
if (el.All(char.IsDigit))
{
result += el;
}
else
{
result += new string(el.Reverse().ToArray());
}
}
Console.WriteLine(result);
}
}
I've used code from stackoverflow.com/a/21123574/1037948 to create a list of Regex matches on line 11:
var list = matchList.Cast<Match>().SelectMany(o =>o.Groups.Cast<Capture>().Skip(1).Select(c => c.Value));

Hey you can do something like:
string test = "test12pop90java989python", tempStr = "", finalstr = "";
var charArray = test.ToCharArray();
for (int i = 0; i < charArray.Length; i++)
{
if (!Char.IsNumber(charArray[i]))
{
tempStr += charArray[i];
}
else
{
char[] ReverseString = tempStr.Reverse().ToArray();
foreach (char charItem in ReverseString)
{
finalstr += charItem;
}
tempStr = "";
finalstr += charArray[i];
}
}
if(tempStr != "" && tempStr != null)
{
char[] ReverseString = tempStr.Reverse().ToArray();
foreach (char charItem in ReverseString)
{
finalstr += charItem;
}
tempStr = "";
}
I hope this helps

How to find biggest substring from string1 into string2

Lets suppose i have two strings string1 and string2.
var string1 = "images of canadian geese goslings";
var string2 = "Canadian geese with goslings pictures to choose from, with no signup needed";
I need to find biggest substring of string1 which matches in string2.
here biggest substring will be "canadian geese" which is matching in string2.
How can I find it? I tried breaking string1 into char[] and find words then merged matched words but that failed my objective.

classy loop approach - the result includes te space after geese "canadian geese "
var string1 = "images of canadian geese goslings";
var string2 = "Canadian geese with goslings pictures to choose from, with no signup needed";
string result = "";
for (int i = 0; i < string1.Length; i++)
{
for (int j = 0; j < string1.Length - i; j++)
{
//add .Trim() here if you want to ignore space characters
string searchpattern = string1.Substring(i, j);
if (string2.IndexOf(searchpattern, StringComparison.OrdinalIgnoreCase) > -1 && searchpattern.Length > result.Length)
{
result = searchpattern;
}
}
}
https://dotnetfiddle.net/q3rHjI
Side note:
canadian and Canadian are not equal so you have to use StringComparison.OrdinalIgnoreCase if you want to search case insensitive

Have a look at the following code https://dotnetfiddle.net/aPyw3o
public class Program {
static IEnumerable<string> substrings(string s, int length) {
for (int i = 0 ; i + length <= s.Length; i++) {
var ss = s.Substring(i, length);
if (!(ss.StartsWith(" ") || ss.EndsWith(" ")))
yield return ss;
}
}
public static void Main()
{
int count = 0;
var string1 = "images of canadian geese goslings";
var string2 = "Canadian geese with goslings pictures to choose from, with no signup needed";
string result = null;
for (int i = string1.Length; i>0 && string.IsNullOrEmpty(result); i--) {
foreach (string s in substrings(string1, i)) {
count++;
if (string2.IndexOf(s, StringComparison.CurrentCultureIgnoreCase) >= 0) {
result = s;
break;
}
}
}
if (string.IsNullOrEmpty(result))
Console.WriteLine("no common substrings found");
else
Console.WriteLine("'" + result + "'");
Console.WriteLine(count);
}
}
The substrings method returns all substrings of the string s with the length of length (for the yield have a look at the documentation https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/yield) We skip substrings that start or end with a space, as we don't want whitespaces to make a substring longer than it really is)
The outer loop iterates through all the possible length values for the substrings, from the longest (ie string1.Length) to the shortest (ie 1). Then for each of the found substrings of length i is checked, if it's also a substring of string2. If that's the case, we can stop, as there cannot be any longer common substring, because we checked all longer substrings in previous iterations. But of course there may be other common substrings with length i

I'm going to add one more, using span/readonlymemory so you can avoid allocating all the strings that the current answers create. Note I didn't do any check for starting space or ending space as that does not seem to be a requirement for the question. This does do a case insensitive search, if you don't want that you can make it more efficient by using the built in indexof and dropping the case insensitive compares.
static void Main(string[] _)
{
var string1 = "images of canadian geese goslings";
var string2 = "Canadian geese with goslings pictures to choose from, with no signup needed";
var longest = FindLongestMatchingSubstring(string1, string2);
Console.WriteLine(longest);
}
static string FindLongestMatchingSubstring(string lhs, string rhs)
{
var left = lhs.AsMemory();
var right = rhs.AsMemory();
ReadOnlyMemory<char> longest = ReadOnlyMemory<char>.Empty;
for (int i = 0; i < left.Length; ++i)
{
foreach (var block in FindMatchingSubSpans(left, i, right))
{
if (block.Length > longest.Length)
longest = block;
}
}
if (longest.IsEmpty)
return string.Empty;
return longest.ToString();
}
static IEnumerable<ReadOnlyMemory<char>> FindMatchingSubSpans(ReadOnlyMemory<char> source, int pos, ReadOnlyMemory<char> matchFrom)
{
int lastMatch = 0;
for (int i = pos; i < source.Length; ++i)
{
var ch = source.Span[i];
int match = IndexOfChar(matchFrom, lastMatch, ch);
if (-1 != match)
{
lastMatch = match + 1;
int end = i;
while (++end < source.Length && ++match < matchFrom.Length)
{
char lhs = source.Span[end];
char rhs = matchFrom.Span[match];
if (lhs != rhs && lhs != (char.IsUpper(rhs) ? char.ToLower(rhs) : char.ToUpper(rhs)))
{
break;
}
}
yield return source.Slice(i, end - i);
}
}
}
static int IndexOfChar(ReadOnlyMemory<char> source, int pos, char ch)
{
char alt = char.IsUpper(ch) ? char.ToLower(ch) : char.ToUpper(ch);
for (int i = pos; i < source.Length; ++i)
{
char m = source.Span[i];
if (m == ch || m == alt)
return i;
}
return -1;
}

I am unable to use substring. How can I fix this?

I am trying to see weather the string is in alphabetical order or no and this error pops up
System.ArgumentOutOfRangeException: Index and length must refer to a location within the string.
Parameter name: length
at System.String.Substring(Int32 startIndex, Int32 length)
at Rextester.Program.Main(String[] args)**
public static void Main(string[] args)
{
string str = "bat\ncat\ndog\n";
int c = 0;
for (int i = 0; i < str.Length; i++)
{
if ((str.Substring(i,i + 1).Equals("\n")))
{
c++;
}
}
String[] strArray = new String[c + 1]; //declare with size
int g = 0;
String h = "";
for (int i = 0; i < str.Length; i++)
{
if ((str.Substring(i,i + 1).Equals("\n")))
{
strArray[g] = h;
h = "";
g = g + 1;
}
else
{
h = h + str.Substring(i,i + 1);
}
}
String p = "True";
for (int i = 0; i < g; i++)
{
if (i < (g - 1))
{
String f = strArray[i];
String g2 = strArray[i + 1];
char d = f[0];
char s = g2[0];
int d1 = (int)d;
int s1 = (int)s;
if (d1 > s1)
{
p = "False";
}
}
}
Console.WriteLine(p);
}
}

Not sure about what you are doing in your second loop and why is it so complex. We can do the same like this. Hope this helps.
using System;
public class Program
{
public static void Main()
{
string str = "abcd";
str = str.Replace('\n',' ');
String p = "True";
for (int i = 1; i < str.Length; i++) {
// if element at index 'i' is less
// than the element at index 'i-1'
// then the string is not sorted
if (str[i] < str[i - 1]) {
p = "false";
}
}
Console.WriteLine(p);
}
}

Pay attention to the definition of substring
The substring starts at a specified character position and has a
specified length
Considering your first use of substring, here
for (int i = 0; i < str.Length; i++)
{
if (str.Substring(i, i + 1).Equals("\n"))
{
c++;
}
}
What happens when we get to i=6 here? Substring tries to give you a new string that starts at position i = 6, and is length = 7 characters long. So it tries to give you 7 characters starting from str[6] to str[12]. Well, there is no str[12], so you get an exception.
Its clear that your intent is NOT to get a string that starts at position 6 and is 7 characters long. You want ONE character, so your loop should be this
for (int i = 0; i < str.Length; i++)
{
if (str.Substring(i, 1).Equals("\n"))
{
c++;
}
}
But theres a much simpler way to get your words in alphabetical order using LINQ
string str = "bat\ncat\ndog\n";
//Removes the trailing \n so you don't have one entry that is only whitespace
str = str.Trim();
string[] strSplit = str.Split('\n').OrderBy(x => x[0]).ToArray();
Now all substrings are sorted alphabetically and you can do whatever you want with them

How to find substring from string without using indexof method in C#?

I want to find the position of a substring in a string if present without using any string method including indexof. I tried so much times but failed. Will anybody tell me how to do in C#? We can use .Length operator.

Sorry.. thought this would be a fun exercise for me, so...
Spoiler
class Program
{
static void Main(string[] args)
{
string str = "abcdefg";
string substr = "cde";
int index = IndexOf(str, substr);
Console.WriteLine(index);
Console.ReadLine();
}
private static int IndexOf(string str, string substr)
{
bool match;
for (int i = 0; i < str.Length - substr.Length + 1; ++i)
{
match = true;
for (int j = 0; j < substr.Length; ++j)
{
if (str[i + j] != substr[j])
{
match = false;
break;
}
}
if (match) return i;
}
return -1;
}
}

Assuming this is homework, my suggestion is to bear in mind that a string is an IEnumerable of chars. So you can loop through the characters in your string...

Since any homework that inspired the question is well past due, here's a stab at a reasonably performant answer.
Simply cycling through the larger string, and cycling through the substring comparing each character as one goes takes Θ((n-m+1) m) time where m is the length of the substring, and n the index where the smaller string is found, or if there is no match the length of the larger minus that of the smaller.
There are a few different algorithm that give better performance, which differ among themselves in terms of which cases they work best in. The Knuth-Morris-Pratt algorithm takes Θ(m) to set up and then Θ(n) time to find, because it first creates a table to know how far ahead it can jump on failing to find a match, and on balance this makes for a quicker search.
Consider that if we were looking for "ababcd" and we'd first found "abab…" (possible match so far), if the next character is c we still have a possible match. If it's a we don't have a match, but should jump forward two characters to start looking for a match starting from that. If it's anything else, we should jump ahead five characters and continue looking for there. Preparing the table to tell us how far to jump makes things much faster from then on:
public static int IndexOf(string haystack, string needle)
{
if(haystack == null || needle == null)
throw new ArgumentNullException();
if(needle.Length == 0)
return 0;//empty strings are everywhere!
if(needle.Length == 1)//can't beat just spinning through for it
{
char c = needle[0];
for(int idx = 0; idx != haystack.Length; ++idx)
if(haystack[idx] == c)
return idx;
return -1;
}
if (needle.Length == haystack.Length) return needle == haystack ? 0 : -1;
if (needle.Length < haystack.Length)
{
int m = 0;
int i = 0;
int[] T = KMPTable(needle);
while(m + i < haystack.Length)
{
if(needle[i] == haystack[m + i])
{
if(i == needle.Length - 1)
return m == haystack.Length ? -1 : m;//match -1 = failure to find conventional in .NET
++i;
}
else
{
m = m + i - T[i];
i = T[i] > -1 ? T[i] : 0;
}
}
}
return -1;
}
private static int[] KMPTable(string sought)
{
int[] table = new int[sought.Length];
int pos = 2;
int cnd = 0;
table[0] = -1;
table[1] = 0;
while(pos < table.Length)
if(sought[pos - 1] == sought[cnd])
table[pos++] = ++cnd;
else if(cnd > 0)
cnd = table[cnd];
else
table[pos++] = 0;
return table;
}

Try this:
internal bool SearchWord(string str, string searchKey)
{
int j = 0; bool result = false;
for (int i = 0; i < str.Length; i++)
{
if (searchKey[j] == str[i])
{
j++; //count++;
}
else { j = 0; }
if (j == searchKey.Length)
{
result = true;
break;
}
}
return result;
}

Try this:
public static string BetweenOf(string ActualStr, string StrFirst, string StrLast)
{
return ActualStr.Substring(ActualStr.IndexOf(StrFirst) + StrFirst.Length,
(ActualStr.Substring(ActualStr.IndexOf(StrFirst))).IndexOf(StrLast) + StrLast.Length);
}

string mainString = Console.ReadLine();
string subString = Console.ReadLine();
for (int i = 0; i <= mainString.Length - subString.Length; i++)
{
bool match = true;
for (int j = 0; j < subString.Length && mainString[i + j] != subString[j]; j++)
{
match = false;
}
if (match)
Console.WriteLine(i);
}

public static findindex(String str,String substr)
{
char a[]=str.toCharArray();
char b[]=substr.toCharArray();
int j=0,t=0;
for(int i=0;i<str.length()&&j<substr.length();i++)
{
if(a[i]==b[j])
{
t=i;
j++;
}
else
continue;
}
if(t==0)
return -1;
else
return t-substr.length()+1;
}//in java

Generating an array of letters in the alphabet

Is there an easy way to generate an array containing the letters of the alphabet in C#? It's not too hard to do it by hand, but I was wondering if there was a built in way to do this.

I don't think there is a built in way, but I think the easiest would be
char[] alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();

C# 3.0 :
char[] az = Enumerable.Range('a', 'z' - 'a' + 1).Select(i => (Char)i).ToArray();
foreach (var c in az)
{
Console.WriteLine(c);
}
yes it does work even if the only overload of Enumerable.Range accepts int parameters ;-)

for (char letter = 'A'; letter <= 'Z'; letter++)
{
Debug.WriteLine(letter);
}

char[] alphabet = Enumerable.Range('A', 26).Select(x => (char)x).ToArray();

I wrote this to get the MS excel column code (A,B,C, ..., Z, AA, AB, ..., ZZ, AAA, AAB, ...) based on a 1-based index. (Of course, switching to zero-based is simply leaving off the column--; at the start.)
public static String getColumnNameFromIndex(int column)
{
column--;
String col = Convert.ToString((char)('A' + (column % 26)));
while (column >= 26)
{
column = (column / 26) -1;
col = Convert.ToString((char)('A' + (column % 26))) + col;
}
return col;
}

Assuming you mean the letters of the English alphabet...
for ( int i = 0; i < 26; i++ )
{
Console.WriteLine( Convert.ToChar( i + 65 ) );
}
Console.WriteLine( "Press any key to continue." );
Console.ReadKey();

You could do something like this, based on the ascii values of the characters:
char[26] alphabet;
for(int i = 0; i <26; i++)
{
alphabet[i] = (char)(i+65); //65 is the offset for capital A in the ascaii table
}
(See the table here.) You are just casting from the int value of the character to the character value - but, that only works for ascii characters not different languages etc.
EDIT:
As suggested by Mehrdad in the comment to a similar solution, it's better to do this:
alphabet[i] = (char)(i+(int)('A'));
This casts the A character to it's int value and then increments based on this, so it's not hardcoded.

Note also, the string has a operator[] which returns a Char, and is an IEnumerable<char>, so for most purposes, you can use a string as a char[]. Hence:
string alpha = "ABCDEFGHIJKLMNOPQRSTUVQXYZ";
for (int i =0; i < 26; ++i)
{
Console.WriteLine(alpha[i]);
}
foreach(char c in alpha)
{
Console.WriteLine(c);
}

Surprised no one has suggested a yield solution:
public static IEnumerable<char> Alphabet()
{
for (char letter = 'A'; letter <= 'Z'; letter++)
{
yield return letter;
}
}
Example:
foreach (var c in Alphabet())
{
Console.Write(c);
}

var alphabets = Enumerable.Range('A', 26).Select((num) => ((char)num).ToString()).ToList();

char alphaStart = Char.Parse("A");
char alphaEnd = Char.Parse("Z");
for(char i = alphaStart; i <= alphaEnd; i++) {
string anchorLetter = i.ToString();
}

//generate a list of alphabet using csharp
//this recurcive function will return you
//a string with position of passed int
//say if pass 0 will return A ,1-B,2-C,.....,26-AA,27-AB,....,701-ZZ,702-AAA,703-AAB,...
static string CharacterIncrement(int colCount)
{
int TempCount = 0;
string returnCharCount = string.Empty;
if (colCount <= 25)
{
TempCount = colCount;
char CharCount = Convert.ToChar((Convert.ToInt32('A') + TempCount));
returnCharCount += CharCount;
return returnCharCount;
}
else
{
var rev = 0;
while (colCount >= 26)
{
colCount = colCount - 26;
rev++;
}
returnCharCount += CharacterIncrement(rev-1);
returnCharCount += CharacterIncrement(colCount);
return returnCharCount;
}
}
//--------this loop call this function---------//
int i = 0;
while (i <>
{
string CharCount = string.Empty;
CharCount = CharacterIncrement(i);
i++;
}

4 ways get English alphabet in Console:
public void ShowEnglishAlphabet()
{
var firstLetter = 'a';
var endLetter = 'z';
for (var letter = firstLetter; letter <= endLetter; letter++)
{
Console.WriteLine($"{letter}-{letter.ToString().ToUpper()}");
}
}
public void ShowEnglishAlphabetFromUnicodeTableDecNumber()
{
var firstLetter = 97;
var endLetter = 122;
for (var letterNumberUnicodeTable = firstLetter;
letterNumberUnicodeTable <= endLetter; letterNumberUnicodeTable++)
{
Console.WriteLine($"{(char)letterNumberUnicodeTable}-
{((char)letterNumberUnicodeTable).ToString().ToUpper()}");
}
}
public void ShowEnglishAlphabetUnicodeTableEscapeSequence()
{
var firstLetter = '\u0061';
var endLetter = '\u007A';
for (var letterNumberUnicodeTable = firstLetter;
letterNumberUnicodeTable <= endLetter; letterNumberUnicodeTable++)
{
Console.WriteLine($"{letterNumberUnicodeTable}-
{letterNumberUnicodeTable.ToString().ToUpper()}");
}
}
public void ShowEnglishAlphabetUnicodeTableLinq()
{
var alphabets = Enumerable.Range('a', 26).Select(letter =>
((char)letter).ToString()).ToList();
foreach (var letter in alphabets)
{
Console.WriteLine($"{letter}-{letter.ToUpper()}");
}
}

Unfortunately there is no ready-to-use way.
You can use;
char[] characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();