LeetCode-17- Letter Combinations of a Phone Number（查表/递归）-Medium

class Solution {
public:
vector<string> letterCombinations(string digits) {
vector<string> ans;
int dLen=digits.length();
if(dLen==0){
return ans;
}

vector<string> dictionary={"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};

string s=dictionary[digits[0]-'0'];
//cout<<"s= "<<s<<endl;

for(int i=0;i<s.length();i++){
string t="";
t+=s[i];

if(dLen>=2){
// cout<<"digits.substr(1)= "<<digits.substr(1)<<endl;

vector<string> v=letterCombinations(digits.substr(1));

// cout<<"v.size()= "<<v.size()<<endl;

for(int j=0;j<v.size();j++){
ans.push_back(t+v[j]);
//cout<<"push_back1: "<<t<<endl;
}
}else{
ans.push_back(t);
//cout<<"push_back2: "<<t<<endl;
}
}

return ans;
}
};