leetcode 17. Letter Combinations of a Phone Number

相关问题

17. Letter Combinations of a Phone Number
77. Combinations

Discription

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"].

思路

递归/深度优先搜索。
具体实现包括递归和非递归两种形式。

时间复杂度：?
空间复杂度：?

代码

递归

class Solution {public:    void dfs(vector<string> &res, string str, int i, string &digits, vector<string> &map)    {        // 边界条件        cout << digits.size();        if (i == digits.size())        {            res.push_back(str);            return;        }        // 递归        for (int j = 0; j < map[digits[i] - '0'].size(); j++)            dfs(res, str + map[digits[i] - '0'][j], i + 1, digits, map);    }    vector<string> letterCombinations(string digits) {        vector<string> map = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};        vector<string> res;        string str = "";        if (digits.size() == 0) return res;        dfs(res, str, 0, digits, map);        return res;    }};

非递归

class Solution {public:        vector<string> letterCombinations(string digits) {        vector<string> res;        if (digits.size() == 0) return res;        vector<string> map = { "", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz" };        queue<string> que;        que.push("");                for (int i = 0; i < digits.size(); i++)     // digits中的第i个字符，如"234" 中的 "2"        {            int n = que.size();            for (int j = 0; j < n; j++)             // 队列中的第j个字符串  "abca"            {                string str = map[digits[i] - '0'];                for (int k = 0; k < str.size(); k++)       // digits中的第i个字符映射的字符串中第k个字符 "abc"的 "b"                    que.push(que.front() + str[k]);                que.pop();            }        }        while(!que.empty())        {            res.push_back(que.front());            que.pop();        }        return res;    }};