checking to see if a string contains every letter of the alphabet

[booksnore]

I am writing some code to search for strings that contain every letter
of the alphabet. At the moment I am using the method below to check to
see if a string contains every letter of the alphabet. I wanted to use a
regular expression but I could not find an ‘AND’ operator within the
regular expression – so I need something like match true if string
contains ‘a’ and ‘b’ and ‘c’ and ‘d’ ..etc,etc. If anyone has any
thoughts on how I can provide the check more effectively than I am doing
at the moment the help would be very much appreciated.


private static bool InAlphabet(string text)

{

if(text==null)

{

return false;

}



int count = 97;

bool IsValid = true;

while (IsValid && count < 123)

{

// Cast character from integral type

string regexStr = "(" + (char)count + ")";

Regex regex_x = new Regex(regexStr);

Match m_x = regex_x.Match(text);

IsValid = m_x.Success;

count++;

}
return IsValid;

}

 

[Ignacio Machin \( .NET/ C# MVP \)]

Hi,

I would do this, I will create a Hash with the letters (char) as key and
value 0 as values.
I will iterate in the chars of the string and set the value
somethins like this:

Hashtable hash = new Hashtable();

hash['a']=0;
hash['b']=0;
hash['c']=0;
....

foreach( char c in string.ToCharArray() )
hash[ c ] = 1;

foreach( int i in hash.Values )
if ( 0 == i )
return false;

return true;


cheers,

 

[Guest]

Using a bitmap might be more efficient than allocating a hash table ...


const int CC_A = (int)'A'; // 65
const int CC_Z = (int)'Z'; // 90
const uint ONE = 0x01;
const uint MAX = 0xFFFFFFFF; // UInt32.MaxValue

string str = "abcdefghijklmnopqrstuvwxyz";

uint map = 4227858432; // first 26 bits OFF

int cc = 0; // char code

foreach (char ch in str)
{
cc = (int)Char.ToUpper(ch);

if (cc >= CC_A && cc <= CC_Z)
{
// In one line ...
// map |= (ONE << (cc - CC_A));

// Step by step...

// Subtract 65 from the char code so the mask fits in 32 bits
//
cc -= CC_A;

// Create the mask by shifting 1 bit the appropriate number of places
//
uint mask = ONE << cc;

// Reassign the bitmap
//
map |= mask;
}
}

if (map == MAX)
{
// TRUE, string contains all 26 alphabet chars
}

Hi,

I would do this, I will create a Hash with the letters (char) as key and
value 0 as values.
I will iterate in the chars of the string and set the value
somethins like this:

Hashtable hash = new Hashtable();

hash['a']=0;
hash['b']=0;
hash['c']=0;
....

foreach( char c in string.ToCharArray() )
hash[ c ] = 1;

foreach( int i in hash.Values )
if ( 0 == i )
return false;

return true;


cheers,

--
Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation

I am writing some code to search for strings that contain every letter
of the alphabet. At the moment I am using the method below to check to
see if a string contains every letter of the alphabet. I wanted to use a
regular expression but I could not find an 'AND' operator within the
regular expression - so I need something like match true if string
contains 'a' and 'b' and 'c' and 'd' ..etc,etc. If anyone has any
thoughts on how I can provide the check more effectively than I am doing
at the moment the help would be very much appreciated.


private static bool InAlphabet(string text)

{

if(text==null)

{

return false;

}



int count = 97;

bool IsValid = true;

while (IsValid && count < 123)

{

// Cast character from integral type

string regexStr = "(" + (char)count + ")";

Regex regex_x = new Regex(regexStr);

Match m_x = regex_x.Match(text);

IsValid = m_x.Success;

count++;

}
return IsValid;

}

 

[Jon Skeet [C# MVP]]

Using a bitmap might be more efficient than allocating a hash table ...

Indeed - not as easy to understand the code as using a boolean array,
however:

static bool ContainsAllLetters(string x)
{
bool[] letters = new bool[26];

int lettersFound=0;

foreach (char c in x)
{
int index = char.ToUpper(c)-'A';

if (index >= 0 &&
index < letters.Length &&
!letters[index])
{
letters[index]=true;
lettersFound++;
}
}

return (lettersFound==letters.Length);
}

Note that this won't spot characters which have accents etc - but at
least it doesn't fail if you include any numbers.

 

[Guest]

An improvement both of us missed ... each loop should probably test whether
our TRUE condition has been met so we don't continue iterating the string
unnecessarily.

Using a bitmap might be more efficient than allocating a hash table ...

Indeed - not as easy to understand the code as using a boolean array,
however:

static bool ContainsAllLetters(string x)
{
bool[] letters = new bool[26];

int lettersFound=0;

foreach (char c in x)
{
int index = char.ToUpper(c)-'A';

if (index >= 0 &&
index < letters.Length &&
!letters[index])
{
letters[index]=true;
lettersFound++;
}
}

return (lettersFound==letters.Length);
}

Note that this won't spot characters which have accents etc - but at
least it doesn't fail if you include any numbers.

 

[booksnore]

Thank you for the replies, they are extremely helpful.