Given two alphabet strings str1 and str2. you can change the characters in str1 to any alphabet characters in order to transform str1 to str2. one restriction is, in each operation, you should change all the same characters simultaneously. what's more, you may use another special character * if necessary, which means during each operations, you may change the same alphabet characters to *, or change all * to a specific character. note that "turn the same characters to *" and "turn all * to a specific character" both take exact one operation.