C solution

int main() {

/* Enter your code here. Read input from STDIN. Print output to STDOUT */
int t,x;
scanf("%d",&t);
for(x=0;x<t;x++)
{
    int first[26]={0},second[26]={0};
    int count=0;
    char str[10000];
    scanf("%s",str);
    int i,k=strlen(str)-1;
     if(strlen(str)%2==1)
        count=-1;
    else
    {
        i=0;
        while(i<strlen(str)/2)
        {
            first[str[i++]-'a']++;
            second[str[k--]-'a']++;
        }
        for(i=0;i<26;i++)
        {

            if(first[i]>second[i]&&first[i]!=0)
                count+=abs(first[i]-second[i]);
        }
    }
     printf("%d\n",count);
}
return 0;

}