九宮格鍵盤輸入

九宮格鍵盤輸入

Letter Combinations of a Phone Number

• 給定一個數字字符串，返回數字可能表明的全部可能的字母組合。

• 數字到字母的映射（就像九宮格電話按鈕同樣）以下圖。

• Given a digit string, return all possible letter combinations that the number could represent.

• A mapping of digit to letters (just like on the telephone buttons) is given below.

Note:
Although the above answer is in lexicographical order, your answer could be in any order you want.

example 1

Input:Digit string "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

思路

1. 以23爲例，2表明abc，只須要將其轉換成lists = [a,b,c]，而後處理3，3爲def，將這三個字符分別加到s的每個元素中，獲得["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]。重複此過程便可。

2. 上述思路能夠用循環完成，同時python提供的reduce函數和生成式特性可以精煉地表述，下面給出兩種代碼。

代碼

class Solution(object):
    def letterCombinations(self, digits):
        """
        :type digits: str
        :rtype: List[str]
        """
        from functools import reduce #python3.x
        if not digits:
            return []
        nums = '0 1 abc def ghi jkl mno pqrs tuv wxyz'.split(' ')
        return reduce(lambda last, d: [x + y for x in last for y in nums[int(d)]], digits, [''])  # 第三個參數是initial



    


    #使用循環完成
    def letterCombinations_old(self, digits):
        if not digits:
            return []
        nums = '0 1 abc def ghi jkl mno pqrs tuv wxyz'.split(' ')
        ret = [_ for _ in nums[int(digits[0])]]
        digits = digits[1:]
        while digits:
            ret = [x + y for x in ret for y in nums[int(digits[0])]]
            digits = digits[1:]
        return ret

本題以及其它leetcode題目代碼github地址: github地址