剑指offer--13题

#include "stdafx.h"
#include <iostream>
using namespace std;
void FirstNoRepeatCh(const char str[], char& ch);

int main(int argc, char* argv[])
{
	const char* str = "cdceasafggsfrrtkkxx";
	char ch = '@';
	FirstNoRepeatCh(str,ch);
	if(ch == '@')
		cout<<"No Find!"<<endl;
	else
		cout<<ch<<endl;
	return 0;
}
//自己编写，即第一种思路
/*void FirstNoRepeatCh(const char str[], char& ch)
{
	int HashTable[256] = {0};
	while(*str != '')
	{
		if(HashTable[*str] == 0)  //用Hash表（哈希表）来判断字符是否重复出现
		{
			char* pch = (char*)(str+1);
			bool chFind = false;

			while(*pch != '' && !chFind)
			{
				if(*str == *pch)
					chFind = true;
				pch++;
			}
			if(chFind)
				HashTable[*str] = 1;
			else
			{
				ch = *str;
				break;
			}
		}
		str++;
	}
}*/
//此为第二种思路+自己编写
void FirstNoRepeatCh(const char str[], char& ch)
{
	if(!str)
		return;
	const int TableSize = 256;
	int HashTable[TableSize] = {0};
	char* pch = (char*)str;
	while(*str != '')
	{
		HashTable[*str]++;
		str++;
	}
	bool chFind = false;
	while(*pch != '' && !chFind)
	{
		if(HashTable[*pch] == 1)
		{
			ch = *pch;
			chFind = true;
		}
		pch++;
	}

}

/*//标准答案
///////////////////////////////////////////////////////////////////////
// Find the first char which appears only once in a string
// Input: pString - the string
// Output: the first not repeating char if the string has, otherwise 0
///////////////////////////////////////////////////////////////////////
char FirstNotRepeatingChar(char* pString)
{
      // invalid input
      if(!pString)
            return 0;   //因为涉及指针，所以判空

      // get a hash table, and initialize it 
      const int tableSize = 256;  //最好用const int
      unsigned int hashTable[tableSize];
      for(unsigned int i = 0; i < tableSize; ++ i)
            hashTable[i] = 0;

      // get the how many times each char appears in the string
      char* pHashKey = pString;
      while(*(pHashKey) != '')
            hashTable[*(pHashKey++)] ++;

      // find the first char which appears only once in a string
      pHashKey = pString;
      while(*pHashKey != '')
      {
            if(hashTable[*pHashKey] == 1)
                  return *pHashKey;

            pHashKey++;
      }

      // if the string is empty 
      // or every char in the string appears at least twice
      return 0;
} */

//注意：根据评论可知，若第二次遍历Hash表，则会得到仅出现一次的最小字符