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 (48.02%)
 * Likes:    4785
 * Dislikes: 458
 * Total Accepted:    702.5K
 * Total Submissions: 1.5M
 * Testcase Example:  '"23"'
 *
 * 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'].
 *
 *
 */

// @lc code=start
/**
 * @param {string} digits
 * @return {string[]}
 */
var letterCombinations = function (digits) {
  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"] };
  let results = [];
  for (let i = 0; i < digits.length; i++) {
    const tempChar = digits.charAt(i);
    if (results.length === 0) results = results.concat(map[tempChar]);
    else {
      const length = results.length;
      for (let j = 0; j < length; j++) {
        const letters = map[tempChar];
        const str = results.shift(0);
        for (let k = 0; k < letters.length; k++) {
          results.push(str + letters[k]);
        }
      }
    }
  }
  return results;
};
// @lc code=end