Remove characters from the first string which are present in the second string | GeeksforGeeks

Write an efficient C function that takes two strings as arguments and removes the characters from first string which are present in second string (mask string).
Key Point: char[256], hashtable, use space for time trade-off.
From Coding Interviews: Questions, Analysis & Solutions
void DeleteCharacters(char* pString, char* pCharsToBeDeleted) {
    int hashTable[256];
    const char* pTemp = pCharsToBeDeleted;
    char* pSlow = pString;
    char* pFast = pString;

    if(pString == NULL || pCharsToBeDeleted == NULL)
        return;

    memset(hashTable, 0, sizeof(hashTable));
    while (*pTemp != '\0') {
        hashTable[*pTemp] = 1;
        ++ pTemp;
    }

    while (*pFast != '\0') {
        if(hashTable[*pFast] != 1) {
            *pSlow = *pFast;
            ++ pSlow;
        }
        ++pFast;
    }

    *pSlow = '\0';
}
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