[LeetCode-Algorithms-17] "Letter Combinations of a Phone Number" (2017.10.12-WEEK6)

题目链接：Letter Combinations of a Phone Number

• 题目描述：
  

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.

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(1)思路:把每个按键上的字母先保存下来，然后读取输入的字符串，对于要求解的数字，暴力循环求解即可。

(2)代码：

class Solution {public:    vector<string> letterCombinations(string digits) {        vector<string> bot, ans, tmp;        bot.push_back("");        bot.push_back("");        bot.push_back("abc");        bot.push_back("def");        bot.push_back("ghi");        bot.push_back("jkl");        bot.push_back("mno");        bot.push_back("pqrs");        bot.push_back("tuv");        bot.push_back("wxyz");        for (int i = 0; i < bot[digits[0] - '0'].size(); i++) {            char c = bot[digits[0] - '0'][i];            string str;            stringstream stream;            stream << c;            str = stream.str();            ans.push_back(str);        }        for (int i = 1; i < digits.length(); i++) {            tmp = ans;            ans.clear();            for (int k = 0; k < tmp.size(); k++) {                for (int j = 0; j < bot[digits[i] - '0'].size(); j++) {                    ans.push_back(tmp[k] + bot[digits[i] - '0'][j]);                }            }        }        return ans;    }};

(3)提交结果：