text: class Solution:
      def minSteps(self, s: str, t: str) -> int:
          if len(s)!=len(t): return -1
          c1 = collections.Counter(s)
          c2 = collections.Counter(t)
          res = 0
          for i in set(list(c1.keys()) + list(c2.keys())):
              res += abs(c1[i] - c2[i])
          return res//2;