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： hash && dfs.
void dfs(vector<string>& out, string ans, int curDepth, string& digits, string map[10] ){
if(curDepth == digits.length()){
out.push_back(ans);
return;
}
for(int i = 0; i < map[digits[curDepth]-‘0‘].length(); ++i){
ans.push_back(map[digits[curDepth]-‘0‘][i]);
dfs(out, ans, curDepth+1, digits, map);
ans.pop_back();
}
}
class Solution {
public:
vector<string> letterCombinations(string digits) {
vector<string> out;
string ans;
string map[10] = {"", "", "abc","def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
dfs(out, ans, 0, digits, map);
return out;
}
};
69. Letter Combinations of a Phone Number
原文：http://www.cnblogs.com/liyangguang1988/p/3961295.html