Python3 concise solution with stack beats 95%
\tclass Solution:\n\t\tdef smallestSubsequence(self, text: str) -> str:        \n\t\t\tdict={}\n\t\t\tfor i in range(len(text)):\n\t\t\t\tdict[text[i]]=i\n\t\t\
\tclass Solution:\n\t\tdef smallestSubsequence(self, text: str) -> str:        \n\t\t\tdict={}\n\t\t\tfor i in range(len(text)):\n\t\t\t\tdict[text[i]]=i\n\t\t\tstack=[]\n\t\t\tfor i in range(len(text)):\n\t\t\t\tif text[i] in stack:\n\t\t\t\t\tcontinue\n\t\t\t\twhile stack and stack[-1]>text[i] and dict[stack[-1]]>i:\n\t\t\t\t\t\tstack.pop()\n\t\t\t\tif text[i] not in stack:\n\t\t\t\t\tstack.append(text[i])\n\t\t\treturn \'\'.join(stack)
['Stack', 'Python3']