C++ MyProgrammingLab problem: Implement the function below //return true iff the

Question

C++ MyProgrammingLab problem:

Implement the function below
//return true iff the letters in s form a subset of the letters in t .

// e.g. "bbcaca", "abba","bcda", "dd" and "bbbaaaa" are subsets of "abcd".

// Unlike for bags, we care only if a letter occurs in the word, not how many times it occurs.

// For example, if you want to find a word s that only contains vowels you could check whether s is a subset of "aeiou". Using the words.txt file and minimum length 3, you would get five hits: "aia", "eau", "euoi", "euouae" and "iou".

//precondition: s and t contain only lowercase letters {'a'... 'z'}
bool isSubSet(const string &s, const string &t) ;

Do not write the entire program or any other functions.

Here is my solution:

bool isSubSet(const string &s, const string &t)
{
   int i = 0, j = 0;
   int k = s.length()-1;
   while(t[i])
   {
       if(t[i] == s[j])
       {
           i++;
           j++;
       }
       else
       {
           i++;
       }
   }
   if(j == k)
   {
       return true;
   }
   else
   {
       return false;
   }
}

MyProgrammingLab is not accepting this answer: It also gave me some hints that I should consider:

?     You almost certainly should be using: '
     ?     You almost certainly should be using: a
     ?     You almost certainly should be using: for

Can someone post the correct solution for this problem?

Explanation / Answer

// Check working code sample here: http://ideone.com/jcR59a

bool isSubSet(const string &s, const string &t)
{
    int diff_s[26] = {0};
    int diff_t[26] = {0};
   for(int i=0; i<t.length(); i++)
   diff_t[t[i]-'a']++;
   for(int i=0; i<s.length(); i++) {
   if(diff_t[s[i]-'a']==0)
   return false;
   }
   return true;
}

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