标签：
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.
Analyse: Be careful about the difference between empty string and non-empty string when conducting an operation. If you set an empty string, you don‘t have an access to any index, the only operation you can do is contat/‘+‘.
Runtime: 4ms
1 class Solution { 2 public: 3 vector<string> letterCombinations(string digits) { 4 vector<string> result; 5 if(digits.empty()) return result; 6 7 string temp(digits.size(), 0); 8 helper(digits, result, temp, 0); 9 return result; 10 } 11 12 void helper(string digits, vector<string>& result, string temp, int depth){ 13 if(depth == digits.size()){ 14 result.push_back(temp); 15 return; 16 } 17 18 string info[] = {" ", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"}; 19 string current = info[digits[depth] - ‘0‘]; //the size of the current string that the digit represent 20 for(int i = 0; i < current.size(); i++){ 21 temp[depth] = current[i]; 22 helper(digits, result, temp, depth + 1); 23 } 24 } 25 };
Letter Combinations of a Phone Number
标签：
原文地址：http://www.cnblogs.com/amazingzoe/p/4873347.html
