第一次只出现一次的字符

#include <stdio.h>
#include <iostream>
using namespace std;
//第一次只出现一次的字符
//input: abaccdeff
//output: b

char FirstNotRepeatingChar1(char* pString);
char FirstNotRepeatingChar2(char* str);

int main()
{
	char* str = "abaccdeff";
	cout<<FirstNotRepeatingChar1(str)<<endl;

	cout<<FirstNotRepeatingChar2(str)<<endl;
	return 0;
}

//时间复杂度为O(n2)
char FirstNotRepeatingChar1(char* str)
{
	int len = strlen(str);
	for(int i=0; i<len-1; i++)
	{
		int j = i + 1;
		for(; j<len; j++)
		{
			if(str[i] == str[j])
				break;
		}
		if(j == len)
			return str[i];
	}
	return '\0';
}

//时间复杂度度O(n)，空间复杂度O(1)
char FirstNotRepeatingChar2(char* pString)
{
	if(pString == NULL)
		return '\0';
	const int tableSize = 256;
	unsigned int hashTable[tableSize];

	for(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';
}