text: class Solution {
  public:
  	// It runs 8ms. A very good solutions from discuss.
      bool isIsomorphic(string s, string t) {
          int a1[256] = {0}, a2[256] = {0}, n = s.size();
          for (int i = 0; i < n; ++i) {
              if (a1[s[i]] != a2[t[i]])   return false;
              a1[s[i]] = i + 1;
              a2[t[i]] = i + 1;
          }
          return true;
      }
  };