first unique character in characters

class Solution {
    
public:
    int firstUniqChar(string s) {
    
        
       int count[256]={
    0};
       int size=s.size();
       //记录每个数字出现的次数
       for(int i=0;i<size;i++)
       {
    
           count[s[i]]+=1;
       }

       //Found only once is digital
       for(int j=0;j<size;j++)
       {
    
           if(1==count[s[j]])
           {
    
               return j;
           }
       }
       return -1;

    }
};

解法二:

class Solution {
    
public:
    int firstUniqChar(string s) {
    
        for(int i=0;i<s.size();i++)
        {
    
            if(s.find(s[i])==s.rfind(s[i]))
            {
    
                return i;
            }
        }
        return -1;
    }
};

解法三:利用哈希表

class Solution {
    
public:
    int firstUniqChar(string s) {
    
        //创建一个哈希表
        map<char,int>v;//Record the number of characters and character appear
        for(int i=0;i<s.size();i++)
        {
    
            ++v[s[i]];
        }
    map<char,int>::const_iterator it=v.begin();
    for(int i=0;i<s.size();i++)
    {
    
        if(v[s[i]]==1)
        {
    
            return i;
        }
        
    }
     return -1;
    }

如有错误,多多指教！