【leetcode】1271. Hexspeak

题目如下：

A decimal number can be converted to its Hexspeak representation by first converting it to an uppercase hexadecimal string, then replacing all occurrences of the digit 0 with the letter O, and the digit 1 with the letter I.  Such a representation is valid if and only if it consists only of the letters in the set {"A", "B", "C", "D", "E", "F", "I", "O"}.

Given a string num representing a decimal integer N, return the Hexspeak representation of N if it is valid, otherwise return "ERROR". 

Example 1:

Input: num = "257"
Output: "IOI"
Explanation:  257 is 101 in hexadecimal.

Example 2:

Input: num = "3"
Output: "ERROR"

Constraints:

• 1 <= N <= 10^12
• There are no leading zeros in the given string.
• All answers must be in uppercase letters.

解题思路：转成十六进制后，把0/1分别替换成O/I，然后检查字符串中是否包含 "A", "B", "C", "D", "E", "F", "I", "O" 以外的字符。

代码如下：

class Solution(object):
    def toHexspeak(self, num):
        """
        :type num: str
        :rtype: str
        """
        num = hex(int(num))[2:]
        num = num.upper()
        num = num.replace('0','O')
        num = num.replace('1', 'I')
        valid = ["A", "B", "C", "D", "E", "F", "I", "O"]
        for i in num:
            if i not in valid:return "ERROR"
        return num