2351. First Letter to Appear Twice

class Solution {
public:
    char repeatedCharacter(string s) {

       for( int i=0; i<s.length(); i++)
       {
           for( int j=i; j>=0; j--)
           {
               if(s[i]==s[j] && i!=j)
               {
                  return s[i];
               }
           }
       } 
      return -1;
    }
};