letter-combinations-of-a-phone-number

最新推荐文章于 2020-04-23 22:58:57 发布

原创最新推荐文章于 2020-04-23 22:58:57 发布 · 356 阅读

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本文介绍了一种使用递归算法来解决电话号码对应的字母组合问题的方法。通过建立数字到字母的映射表，程序能够根据输入的数字字符串返回所有可能的字母组合。

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题目：

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.
这里写图片描述

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.

程序：

class Solution {
public:
      vector<string> res;
    string tmp;
    map<int, string> num2alp = {{2, "abc"}, {3, "def"}, {4, "ghi"}, {5, "jkl"}, {6, "mno"}, {7, "pqrs"}, {8, "tuv"}, {9,"wxyz"}};
    vector<string> letterCombinations(string digits) {
        if(digits.empty()){
            res.push_back(tmp);
            return res;
        }
        else
            getStr(digits, 0, tmp);
        return res;

    }
    void getStr(string digits, int idx, string tmp){
        if(idx == digits.size())
            res.push_back(tmp);
        int im = digits[idx] - '0';
        for(int i = 0; i < num2alp[im].size(); ++i){
            getStr(digits, idx + 1, tmp + num2alp[im][i]);
        }
    }
};

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