Determine if a word or phrase is an isogram. An isogram (also known as a "nonpattern word") is a word or phrase without a repeating letter, however spaces and hyphens are allowed to appear multiple times. Examples of isograms: lumberjacks background downstream six-year-old The word isograms, however, is not an isogram, because the s repeats.

isogram.c

#include "isogram.h"
#include "string.h"
#include "ctype.h"

// simple Key/Value struct
struct Map {
    int Key;
    int Value;
};

bool is_isogram(const char phrase[])
{	
	// check if the input is NULL
	if (phrase == 0) return false;
	// we need to get the size of our string
	int word_len = strlen(phrase); 
	// we need to make it a char and not a const char
	char temp[word_len + 1];
	strcpy(temp, phrase);
	// we also loop though and make everything lowercase
	for(int i = 0; temp[i]; i++){
	  temp[i] = tolower(temp[i]);
	}
	// we inialize a freq map
	struct Map freqMapArray[word_len];
	// add all values to map list in int form (no need to deal with chars)
	for(int i = 0; temp[i] != '\0'; i++) {
		struct Map freq;
	    const char character = temp[i];
	    freq.Key = character - '\x00';
	    freq.Value = 0;
	    freqMapArray[i] = freq;
	}
	// we could be smarter and check the values as we add them to our freq 
	// lookup Map Array - but for simplicty we build them, then
	// loop over our map
	for (int i = 0; i < word_len; ++i)
	{
		// pull the vars out as that we saved above
		struct Map b = freqMapArray[i];
		// loop over map for each var
		for (int i = 0; i < word_len; ++i)
		{
			// pull the values out of the list
			struct Map c = freqMapArray[i];
			if (b.Key == c.Key)
			{
				switch(b.Key) {
			      case 32: // whitespaces
			      	break;
			      case 45: // - 
			      	break;
			      default : // all others we add to the value
			         b.Value += 1;
				}
			}
			// if we've seen more than one - return false
			if (b.Value > 1 ){
				return false;
			}
		}
	}
	// if we got through all the code above -
	// we havent seen any chars more than once
	return true;
}