[LeetCode] (medium) 17. Letter Combinations of a Phone Number

Frontier_Setter

于 2019-02-02 16:49:10 发布

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分类专栏： LeetCode 文章标签： LeetCode

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本文介绍了一个经典的编程问题：给定一个包含2到9的数字字符串，返回所有可能的字母组合，这些组合由数字对应的电话按键上的字母组成。例如，输入'23'，输出['ad', 'ae', 'af', 'bd', 'be', 'bf', 'cd', 'ce', 'cf']。文章详细解释了使用广度优先搜索算法解决此问题的方法。

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Given a string containing digits from 2-9 inclusive, 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. Note that 1 does not map to any letters.

Example:
Input: "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.

广搜，但是输入的size == 0的情况是真的烦，总是忘记处理。

class Solution {
public:
    vector<string> letterCombinations(string digits) { 
        queue<string> Q;
        vector<string> result;
        Q.push("");
        
        vector<vector<char>> map_table = {{' '},{}, {'a', 'b', 'c'}, {'d', 'e', 'f'}, {'g', 'h', 'i'},
                                          {'j', 'k', 'l'}, {'m', 'n', 'o'}, {'p', 'q', 'r', 's'},
                                          {'t', 'u', 'v'}, {'w', 'x', 'y', 'z'}};
        if(digits.size() == 0) return result;
        
        string cur;
        
        while(!Q.empty()){
            cur = Q.front();
            Q.pop();
            if(cur.size() == digits.size()){
                result.push_back(cur);
            }else{
                int num = digits[cur.size()]-'0';
                for(int i = 0; i < map_table[num].size(); ++i){
                    Q.push(cur+map_table[num][i]);
                }
            }
        }
        return result;
    }
};