其實我一開始讀不懂題目。。我以為應該是出來的答案應該都是兩位的，我還特地拷貝AC程式碼執行一下才知道題目意思= =雖然看了懂了題意還是不會做 程式碼挺容易懂的，運用遞迴，以level為digits的遍歷指標，在遍歷每個指標對應的text組成out,總的來說是DFS的運用

class Solution {
public:
	vector<string> letterCombinations(string digits) {
		string text[] = { "abc","def","ghi","jkl","mno","pqrs","tuv","wxyz" };
		vector<
 
string>ans;
		if (digits.empty())return ans;
		string out = "";
		letterConmbinationsDFS(digits, text, 0, out, ans);
		return ans;
	}
	void letterConmbinationsDFS(string digits, string text[], int level, string out,
		vector<string>& ans) {
		if (level == digits.size())ans.push_back(out)
 
;
		else {
			string str = text[digits[level] - '2'];
			for (int i = 0; i < str.size(); ++i) {
				out.push_back(str[i]);
				letterConmbinationsDFS(digits, text, level + 1, out, ans);
				out.pop_back();
			}
		}
	}
};