Letter Combinations of a Phone Number

本文介绍了一种使用递归深度优先搜索的方法来实现电话按键对应字母的所有可能组合。通过定义字符串数组来映射电话按键上的字母,并利用递归函数进行遍历组合,最终将所有可能的组合存入结果向量中。

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class Solution {
public:
    string dic[10] = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
    vector<string> res;

    void dfs(string& digits, string s, int cur, int len){
        if(cur==len){
            res.push_back(s);
            return;
        }
        int c = digits[cur] - '0';
        for(int i = 0; i < dic[c].size(); i++){
            s.push_back(dic[c][i]);
            dfs(digits, s, cur + 1, len);
            s.pop_back();
        }

        return;
    }

    vector<string> letterCombinations(string digits) {
        const int len = digits.length();
        if(len == 0) return res;
        string s;
        dfs(digits, s, 0, len);
        return res;
    }
};
(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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