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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.
思路：回溯
class Solution { public: vector<string> letterCombinations(string digits) { vector<string> lux(10); lux[2] = "abc"; lux[3] = "def"; lux[4] = "ghi"; lux[5] = "jkl"; lux[6] = "mno"; lux[7] = "pqrs"; lux[8] = "tuv"; lux[9] = "wxyz"; vector<string> ans; if(digits.empty()) { ans.push_back(""); return ans; } string X = digits; vector<int> S(digits.length()); int k = 0; while(k >= 0) { while(k >= 0 && S[k] < lux[digits[k] - ‘0‘].length()) { X[k] = lux[digits[k] - ‘0‘][S[k]++]; if(k < digits.length() - 1) { k++; } else { ans.push_back(X); //当判断条件是 （长度 - 1） 时不需要 k-- 因为最后一位数字需要循环 } } S[k] = 0; k--; } if(ans.empty()) { ans.push_back(""); return ans; } return ans; } };
【leetcode】 Letter Combinations of a Phone Number(middle)
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原文地址：http://www.cnblogs.com/dplearning/p/4206040.html
