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Javascript(leetcode#17) Letter Combinations of a Phone Number

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Difficult:Medium

題目

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.

A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.

example

翻譯

給定一個包含 2-9 數字的字符串，返回該數字可以表示的所有可能的字母組合。以任意順序返回答案。

下面給出了數字到字母的映射（就像在電話按鈕上一樣）。請注意，1 不映射到任何字母。

範例

Example 1

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Input: digits = "23"
Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]

Example 2

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Input: digits = ""
Output: []

Example 3

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Input: digits = "2"
Output: ["a","b","c"]

解題思路

1.可將組合分解成較小的組合case
2.再一較小的組合case一層層增加

Solution

Code 1 :

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var letterCombinations = function(digits) {
    let obj={
        "2":"abc",
        "3":"def",
        "4":"ghi",
        "5":"jkl",
        "6":"mno",
        "7":"pqrs",
        "8":"tuv",
        "9":"wxyz"
    }
    let combs=digits?[""]:[];
    for(let digit of digits){
        let newval=[];
       for(let comb of combs){
          for(let objitem of obj[digit]){
            newval.push(comb+objitem);
          }
       }
       combs=newval;
    }
    return combs;
};