Leetcodes Solutions 17 Letter Combinations of a Phone Number

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Given a digit string, 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.

Input:Digit string "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.

思路1

用一張表存儲數字對應的字元串。然後用分步乘法原理。利用一個tempres來保存當前的排列。

class Solution{public: vector<string> letterCombinations(string digits){ vector<string> res; if (digits.size() == 0) return res; string charmap[10] = {"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"}; res.push_back(""); for(int i =0; i < digits.size(); i++){ vector<string> tempres; string chars = charmap[digits[i] - 0]; for(int c = 0; c < chars.size(); c++) for(int j = 0; j < res.size(); j++) tempres.push_back(res[j] + chars[c]); res = tempres; } return res; }};

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