Letter Combinations of a Phone Number

iven 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"].

对“0”的情况特殊处理；对digits对应的字符打表；然后递归枚举求解

class Solution {
public:
vector<char> temp;
vector< vector<char> > ans;
string s[9] = {"","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
void get_str(string digits, int index, int count)
{

if(temp.size() == count)
{
ans.push_back(temp);
return;
}
if(index >= count)
return;
int i ,j;
for(i = 0;i<s[digits[index]-'0'-1].length();i++)
{

temp.push_back(s[digits[index]-'0'-1][i]);
get_str(digits,index+1,count);
temp.pop_back();
}
}

vector< string > letterCombinations(string digits) {
int i,j = 0;
string num;
vector< string > ans1;
int len = 0;
if(digits == "")
return ans1;
for(i = 0;i<digits.length();i++)
{
if(digits[i] != '0')
{
num= num +digits[i];
len++;
}
}

get_str(num,0,len);

for(i = 0;i<ans.size();i++)
{
string temp1;
for(j = 0;j<ans[i].size();j++)
temp1 = temp1 + ans[i][j];
ans1.push_back(temp1);
}
return ans1;
}
};