LeetCode: "Letter Combinations of a Phone Number
一些小问题, “”的输出我的是[], 但是答案却是[""], 比较难理解,3次过
1 class Solution { 2 public: 3 void dfs(vector<string> &ret, string tmp, map<char, string> refer, string digits, int beg) { 4 if (beg >= digits.size()) { 5 ret.push_back(tmp); 6 return; 7 } 8 if (digits[beg] <= '9' && digits[beg] >= '2') { 9 for (int i = 0; i < refer[digits[beg]].size(); i++) { 10 string r = refer[digits[beg]]; 11 dfs(ret, tmp+r[i], refer, digits, beg+1); 12 } 13 } 14 } 15 vector<string> letterCombinations(string digits) { 16 // Start typing your C/C++ solution below 17 // DO NOT write int main() function 18 map<char, string> refer; 19 refer['2'] = "abc"; 20 refer['3'] = "def"; 21 refer['4'] = "ghi"; 22 refer['5'] = "jkl"; 23 refer['6'] = "mno"; 24 refer['7'] = "pqrs"; 25 refer['8'] = "tuv"; 26 refer['9'] = "wxyz"; 27 vector<string> ret; 28 string tmp = ""; 29 dfs(ret, tmp, refer, digits, 0); 30 return ret; 31 } 32 };
加一个iterative的方法
1 class Solution { 2 public: 3 vector<string> letterCombinations(string digits) { 4 // IMPORTANT: Please reset any member data you declared, as 5 // the same Solution instance will be reused for each test case. 6 map<char, string> S; 7 S['2'] = "abc", S['3'] = "def", S['4'] = "ghi", S['5'] = "jkl"; 8 S['6'] = "mno", S['7'] = "pqrs", S['8'] = "tuv", S['9'] = "wxyz"; 9 queue<string> que; 10 vector<string> res; 11 if (digits.size() == 0) { 12 res.push_back(""); 13 return res; 14 } 15 for (int i = 0; i < S[digits[0]].size(); i++) que.push(string("")+S[digits[0]][i]); 16 while (!que.empty()) { 17 string tmp = que.front(); 18 que.pop(); 19 if (tmp.size() == digits.size()) res.push_back(tmp); 20 else for (int i = 0; i < S[digits[tmp.size()]].size(); i++) que.push(tmp+S[digits[tmp.size()]][i]); 21 } 22 return res; 23 } 24 };
C#
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 public class Solution { 2 public List<string> LetterCombinations(string digits) { 3 Dictionary<char, string> S = new Dictionary<char, string>(); 4 S.Add('2', "abc"); S.Add('3', "def"); S.Add('4', "ghi"); S.Add('5', "jkl"); 5 S.Add('6', "mno"); S.Add('7', "pqrs"); S.Add('8', "tuv"); S.Add('9', "wxyz"); 6 Queue<string> que = new Queue<string>(); 7 List<string> ans = new List<string>(); 8 if (digits.Length == 0) return ans; 9 foreach (var s in S[digits[0]]) que.Enqueue("" + (char)s); 10 while (que.Count != 0) { 11 string peek = que.Peek(); 12 que.Dequeue(); 13 if (peek.Length == digits.Length) ans.Add(peek); 14 else foreach(var s in S[digits[peek.Length]]) que.Enqueue(peek + (char)s); 15 } 16 return ans; 17 } 18 }