unique_chars.cpp

// Assuming we are working with the ASCII character set.  256 unique values.
//
// First, check that the length of the string is under the number of unique values.
// If it is greater, the string does not have all unique characters
//
// Second, create an array of boolean values of size of unique characters.
// Traverse the string and flag the array value from false to true when a character is hit.
// When the character is hit a second time, return false.

bool hasUniqueChars(char * string)
{
   if (strlen(string) > 256)  // Step One
		return false;
	
	int length = strlen(string);
	bool * char_set = new bool[256];
	
	for (int i = 0; i <  length; ++i) // Step Two
	{
		int val = string[i];
		if (char_set[val] == true)    // If the character was already hit
		{	
                    delete char_set;
                    return false;
                }
		char_set[val] = true;
	}
        delete char_set;
	return true;
}