finding if two words are anagrams of each other

Question

I am looking for a method to find if two strings are anagrams of one another.

Ex: string1 - abcde
string2 - abced
Ans = true
Ex: string1 - abcde
string2 - ab         


        

Answer 1

Using an ASCII hash-map that allows O(1) look-up for each char.

The java example listed above is converting to lower-case that seems incomplete. I have an example in C that simply initializes a hash-map array for ASCII values to '-1'

If string2 is different in length than string 1, no anagrams

Else, we update the appropriate hash-map values to 0 for each char in string1 and string2

Then for each char in string1, we update the count in hash-map. Similarily, we decrement the value of the count for each char in string2.

The result should have values set to 0 for each char if they are anagrams. if not, some positive value set by string1 remains

#include 
#include 
#include 

#define ARRAYMAX 128

#define True        1
#define False       0

int isAnagram(const char *string1, 
            const char *string2) {

    int str1len = strlen(string1);
    int str2len = strlen(string2);

    if (str1len != str2len) /* Simple string length test */
        return False;

    int * ascii_hashtbl = (int * ) malloc((sizeof(int) * ARRAYMAX));
    if (ascii_hashtbl == NULL) {
        fprintf(stderr, "Memory allocation failed\n");
        return -1;
    }
    memset((void *)ascii_hashtbl, -1, sizeof(int) * ARRAYMAX);
    int index = 0;
    while (index < str1len) { /* Populate hash_table for each ASCII value 
                                in string1*/
        ascii_hashtbl[(int)string1[index]] = 0;
        ascii_hashtbl[(int)string2[index]] = 0;
        index++;
    }
    index = index - 1;
    while (index >= 0) {
        ascii_hashtbl[(int)string1[index]]++; /* Increment something */
        ascii_hashtbl[(int)string2[index]]--; /* Decrement something */
        index--;
    }
    /* Use hash_table to compare string2 */
    index = 0;
    while (index < str1len) {
        if (ascii_hashtbl[(int)string1[index]] != 0) {
            /* some char is missing in string2 from string1 */
            free(ascii_hashtbl);
            ascii_hashtbl = NULL;
            return False;
        }
        index++;
    }
    free(ascii_hashtbl);
    ascii_hashtbl = NULL;
    return True;
}

int main () {
    char array1[ARRAYMAX], array2[ARRAYMAX];
    int flag;

    printf("Enter the string\n");
    fgets(array1, ARRAYMAX, stdin);
    printf("Enter another string\n");
    fgets(array2, ARRAYMAX, stdin);

    array1[strcspn(array1, "\r\n")] = 0;
    array2[strcspn(array2, "\r\n")] = 0;
    flag = isAnagram(array1, array2);
    if (flag == 1)
        printf("%s and %s are anagrams.\n", array1, array2);
    else if (flag == 0)
        printf("%s and %s are not anagrams.\n", array1, array2);

    return 0;
}