UniqueCharSolution

bool unique(string input)
{
    char max = 0;

    foreach(char a in input)                                                    /* Find the value of the largest character in the input string (Complexity of N) */
    {
        if(a > max)
            max = a;
    }
/* Generate a bool array that has a length long enough to store every character code up to the max found in the input string */
    new bool Char_Used[(int) max] = FALSE;

/* Iterate through the string. This loop will have a complexity of N */
    foreach(char c in input)
    {
    /* Use the code for each character to jump to that index in the array (complexity of a constant) */
        if(Char_Used[c])
            return FALSE;   /* If that index has a value of TRUE, then return false because the character is not unique. */

        else
            Char_Used[c] = TRUE;    /* If the index is not already set to TRUE, this is the first appearance of that character so set that index to TRUE in case we see it again */
    }

    return TRUE;                                                                    /* If we get to here, then there are no repeats in the entire string. */
}