// function to return the number of unique
// characters in str[]
int count_unique_char(char* str) {	int hash[128] = { 0 };	int i, c = 0;	// reading each character of str[]	for (i = 0; i < strlen(str); ++i) {	// set the position corresponding	// to the ASCII value of str[i] in hash[] to 1	hash[str[i]] = 1;	}	// counting number of unique characters	// repeated elements are only counted once	for (i = 0; i < 128; ++i) {	c += hash[i];	}	return c;
}