Write a function that takes a string as input and reverse only the vowels of a string.

Example 1:
 Given s = "hello", return "holle".

Example 2:
 Given s = "leetcode", return "leotcede".

Note:
 The vowels does not include the letter "y". 

bool isVowels(char c)
{
    if('a' == c || 'o' == c ||'e' == c ||'i' == c ||'u' == c ||'A' == c || 'O' == c ||'E' == c ||'I' == c ||'U' == c)
        return true;
    else
        return false;
}

int swap(char *a,char *b)
{
    char tmp = *a;
    *a = *b;
    *b = tmp;
    
    return 0;
}

char* reverseVowels(char* s) 
{
    int len = strlen(s);
    int dict[256] = {0};
    dict['a'] = 1, dict['A'] = 1;
    dict['e'] = 1, dict['E'] = 1;
    dict['i'] = 1, dict['I'] = 1;
    dict['o'] = 1, dict['O'] = 1;
    dict['u'] = 1, dict['U'] = 1;
    int start = 0;
    int end = len - 1;
        
    while(start < end)
    {
        while((dict[s[start]]==0)&&(start < end))
        {
            start++;
        }
        
        while((dict[s[end]]==0) &&(start < end))
        {
            end--;
        }
        
        if(start >= end)
            break;
        
        /*exchange*/
        swap(&s[start],&s[end]);
        
        start++;
        end--;
    }
    
    return s;
}

原本判断是否是原因字母时使用的函数，AC之后看到讨论区有人用dict这种形式，相对于函数调用更清晰，减少了函数调用开销。