time O(N) space O(26)

be aware of test case “abcdefghijklmnopqrstuvwxyz” “bcdefghijklmnopqrstuvwxyzq” where a in str1 not exists in str2; z–map-> q; p –map->q

class Solution:
    def canConvert(self, str1: str, str2: str) -> bool:
        if str1 == str2:
            return True
        d = {}
        for i,j in zip(str1,str2):
            d[i] = d.get(i,j)
            if d[i] != j:
                return False
        return len(set(str2)) < 26 # here can't be str1