Leetcode 17 Letter Combinations of a Phone Number

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.
题意为输出所有按键可能表示的字母组合。
因为不知道按键组合有多长，所以可以用搜索来做，

为了效率我用的是BFS，不过好像也没快到哪里去。

先打印出字典表，用队列进行搜索，算法的复杂度最优就行了，不必在意常数项的问题。

class Solution {
public:
vector<string> letterCombinations(string digits) {
string dic[11]={"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
vector<string> result;
queue <string> q;
q.push("");
for(int i=0;i<digits.length();i++)
{
int cnt=q.size();
while(cnt--)
{
string temp=q.front();
q.pop();
for(int j=0;j<dic[digits[i]-'0'].length();j++)
q.push(temp+dic[digits[i]-'0'][j]);
}
}
if(q.front()=="") q.pop();
while(!q.empty())
{
result.push_back(q.front());
q.pop();
}
return result;
}
};