17.letter-combinations-of-a-phone-number.js

/*
 * @lc app=leetcode id=17 lang=javascript
 *
 * [17] Letter Combinations of a Phone Number
 *
 * https://leetcode.com/problems/letter-combinations-of-a-phone-number/description/
 *
 * algorithms
 * Medium (43.14%)
 * Likes:    2609
 * Dislikes: 337
 * Total Accepted:    452.3K
 * Total Submissions: 1M
 * Testcase Example:  '"23"'
 *
 * Given a string containing digits from 2-9 inclusive, 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 that 1 does not map to any letters.
 * 
 * 
 * 
 * Example:
 * 
 * 
 * Input: "23"
 * Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
 * 
 * 
 * Note:
 * 
 * Although the above answer is in lexicographical order, your answer could be
 * in any order you want.
 * 
 */

// @lc code=start
/**
 * @param {string} digits
 * @return {string[]}
 */
var letterCombinations = function (digits) {
    let table = {
        '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'],
    };

    return Array.from(digits).reduce((acc, crr) => {
        if (acc.length > 0) {
            acc = acc.map(com => {
                let newCom = [];
                table[crr].forEach(item => {
                    newCom.push(com + item);
                });
                return newCom;
            });
            acc = [].concat.apply([], acc);
        } else {
            table[crr].forEach(item => {
                acc.push(item);
            });
        }
        return acc;
    }, []);
};
// @lc code=end