comefrom: <doocs>1930.Unique Length-3 Palindromic Subsequences_1.py
code: def countPalindromicSubsequence( s: str) -> int:
      res = 0
      for i in range(26):
          c = chr(ord('a') + i)
          if c in s:
              l, r = s.index(c), s.rindex(c)
              chars = {s[j] for j in range(l + 1, r)}
              res += len(chars)
      return res
masked: def sample_funcname ( var_0 : str ) -> int :
      var_4 = 0
      for var_7 in range ( 26 ) :
          var_11 = chr ( ord ( 'a' ) + var_7 )
          if var_11 in var_0 :
              var_13 , var_15 = var_0.index ( var_11 ) , var_0.rindex ( var_11 )
              var_18 = { var_0 [ var_16 ] for var_16 in range ( var_13 + 1 , var_15 ) }
              var_4 += len ( var_18 )
      return var_4
  