leetCode - Letter Combinations of a Phone Number(backtracking)

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

 

Example 1:

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

Example 2:

Input: digits = "" Output: []

Example 3:

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

 

Constraints:

• 0 <= digits.length <= 4
• digits[i] is a digit in the range ['2', '9'].

 

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풀이

const letterCombinations = function (digits) {
    if (!digits.length) return "";
    let result = [];
    let map = {
        2: ['a', 'b', 'c'],
        3: ['d', 'e', 'f'],
        4: ['g', 'h', 'i'],
        5: ['j', 'k', 'l'],
        6: ['m', 'n', 'o'],
        7: ['p', 'q', 'r', 's'],
        8: ['t', 'u', 'v'],
        9: ['w', 'x', 'y', 'z'],
    };
    function backtrack(str, index) {
        if (index === digits.length) {
            result.push(str);
            return;
        }

        for (v of map[digits[index]]) {
            backtrack(str + v, index + 1);
        }
    }
    backtrack('', 0);

    return result;
};