Coding Interview Questions: No. 13 - First Character Appearing Only Once

Problem: Implement a function to find the first character in a string which only appears once.

For example: It returns ‘b’ when the input is “abaccdeff”.

Use Hashtab, int array: hashTable[256] or bitset to store found info.

char FirstNotRepeatingChar(char* pString)

{

    if(pString == NULL)

        return '\0';

    const int tableSize = 256;

    unsigned int hashTable[tableSize];

    for(unsigned int i = 0; i<tableSize; ++ i)

        hashTable[i] = 0;

    char* pHashKey = pString;

    while(*(pHashKey) != '\0')

        hashTable[*(pHashKey++)] ++;

    pHashKey = pString;

    while(*pHashKey != '\0')

    {

        if(hashTable[*pHashKey] == 1)

            return *pHashKey;

        pHashKey++;

    }

    return '\0';

}

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