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leetcode第18题--Letter Combinations of a Phone Number
Problem：
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"].
Note:
Although the above answer is in lexicographical order, your answer could be in any order you want.
想了半天不知道怎么做，对递归真心不熟悉。特意看了算法导论的两个优先搜索，即广度优先和深度优先 bfs 和 dfs，这题用到的是dfs方法。
void dfs(int len, string s, string t, vector<string> &ans){ string ss[] = {"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"}; if (len == s.size()) // 当t已经存够s长度个的时候就可以push到答案中并返回 { ans.push_back(t); return; } for (int i = 0; i < ss[s[len] -‘0‘].size(); ++i) // 进行深度优先搜索，len相当于depth { dfs(len + 1, s, t + ss[s[len] - ‘0‘][i], ans); }}vector<string> letterCombinations(string digits){ vector<string> ans; ans.clear(); if (digits.size() == 0) { ans.push_back(""); return ans; } dfs(0, digits, "", ans);// 从第零层temp str 为空开始往深处搜索 return ans;}
leetcode第18题--Letter Combinations of a Phone Number
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