【Swords offer】The first character that appears only once

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1. Topic

2. Ideas

      Build a hash table and count the number of occurrences of each character when scanning the string for the first time. The second time the string is scanned, the position of the first character that occurs only once is returned.

3. Code

  1  class Solution {
   2  public :
   3      int FirstNotRepeatingChar( string str) {
   4  
  5          // special input 
  6          if (str.size() == 0) return -1;
   7  
  8          // auxiliary container 
  9          map< char , int > item;
 10  
11          // first traversal of string 
12          for ( int i = 0; i < length; i++)
 13              item[str[i]]++;
 14  
15          // second traversal of string 
16          for (int i = 0; i < length; i++)
 17              if (item[str[i]] == 1)
 18                  return i;
 19  
20          // no one-occurrence character 
21          return -1;
 22      }
 23 };