第一个只出现一次的字符

题目：在一个字符串中找到第一个只出现一次的字符。如输入abaccdeff，则输出b。

分析：这道题是2006年google的一道笔试题。

#include "stdio.h" 



char FirstNotRepeatingChar(char* pString)

{

    unsigned int i;

      // invalid input

      if(!pString)

            return 0;



      // get a hash table, and initialize it 

      const int tableSize = 256;

      unsigned int hashTable[tableSize];

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

            hashTable[i] = 0;



      // get the how many times each char appears in the string

      char* pHashKey = pString;

      while(*(pHashKey) != '\0')

            hashTable[*(pHashKey++)] ++;



      // find the first char which appears only once in a string

      pHashKey = pString;

      while(*pHashKey != '\0')

      {

            if(hashTable[*pHashKey] == 1)

                  return *pHashKey;



            pHashKey++;

      }



      // if the string is empty 

      // or every char in the string appears at least twice

      return 0;

} 

 

 int main()

 { 

     printf("%c",FirstNotRepeatingChar("abaccdeff"));

     return 0;

 }

 

 

例二：字符串其实就是字符数组，上面的例一先来一个小例子

#include "stdio.h" 



char FirstNotRepeatingChar(char* pString)

{

    

      char* pHashKey = pString;

      while(*(pHashKey) != '\0')

      {

              printf("%c\n",*(pHashKey++));

          

      }   

     // find the first char which appears only once in a string     

} 

 

 int main()

 { 

  FirstNotRepeatingChar("abaccdeff");

     return 0;

 }

a

b

c

等