letter-combinations-of-a-phone-number

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]);
        }
    }
};

点评:

使用递归进行解答

(Telephone Number Word Generator) Standard telephone keypads contain the digits 0 through 9. The numbers 2 through 9 each have three letters associated with them, as is indicated by the following table: Many people find it difficult to memorize phone numbers, so they use the correspondence between digits and letters to develop seven-letter words that correspond to their phone numbers. For example, a person whose telephone number is 686-2377 might use the correspondence indi- cated in the above table to develop the seven-letter word “NUMBERS.” Businesses frequently attempt to get telephone numbers that are easy for their clients to remember. If a business can advertise a simple word for its customers to dial, then no doubt the business will receive a few more calls. Each seven-letter word corresponds to exactly one seven-digit telephone number. The restaurant wishing to increase its take-home business could surely do so with the number 825-3688 (i.e., “TAKEOUT”). Each seven-digit phone number corresponds to many separate seven-letter words. Unfortunately, most of these represent unrecognizable juxtaposi- tions of letters. It’s possible, however, that the owner of a barber shop would be pleased to know that the shop’s telephone number, 424-7288, corresponds to “HAIRCUT.” A veterinarian with the phone number 738-2273 would be happy to know that the number corresponds to “PETCARE.” Write a program that, given a seven-digit number, writes to a file every possible seven-letter word corresponding to that number. There are 2187 (3 to the seventh power) such words. Avoid phone numbers with the digits 0 and 1.
06-09
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