LEETCODE17Letter Combinations of a Phone Number《越努力，越幸运》

Letter Combinations of a Phone Number 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’].

class Solution { public: vector<string> str= {"abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"}; vector<string>v; void letterMapping(string d, int f) { int j; static string temp; if (f == d.size()) { v.push_back(temp); return ; } int l = (int)d[f] - '0' - 2; for (j = 0; j < str[l].size(); j++) { temp.push_back(str[l][j]); letterMapping(d, f + 1); temp.pop_back(); } } vector<string> letterCombinations(string digits) { if (digits == "") return v; letterMapping(digits, 0); return v; } };