leetcode/17.电话号码的字母组合.py at master · junncao/leetcode · GitHub

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#
# @lc app=leetcode.cn id=17 lang=python
#
# [17] 电话号码的字母组合
#
# https://leetcode-cn.com/problems/letter-combinations-of-a-phone-number/description/
#
# algorithms
# Medium (50.95%)
# Likes:    438
# Dislikes: 0
# Total Accepted:    43.4K
# Total Submissions: 85.3K
# Testcase Example:  '"23"'
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# 给定一个仅包含数字 2-9 的字符串，返回所有它能表示的字母组合。
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# 给出数字到字母的映射如下（与电话按键相同）。注意 1 不对应任何字母。
#
#
#
# 示例:
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# 输入："23"
# 输出：["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
#
#
# 说明:
# 尽管上面的答案是按字典序排列的，但是你可以任意选择答案输出的顺序。
#
#
class Solution(object):
    def letterCombinations(self, digits):
        """
        :type digits: str
        :rtype: List[str]
        """
        mapping = {'2': 'abc', '3': 'def', '4': 'ghi', '5': 'jkl',
                   '6': 'mno', '7': 'pqrs', '8': 'tuv', '9': 'wxyz'}
        if len(digits) == 0:
            return []
        if len(digits) == 1:
            return mapping[digits[0]]
        pre=self.letterCombinations(digits[:-1])
        additional=mapping[digits[-1]]
        return [p+a for p in pre for a in additional]