Given numbers only a 2-9 string, it returns all letter combinations indicated.
Given digital map to letters as follows (the same telephone key). Note 1 does not correspond to any alphabet.
Example:
输入："23"
输出：["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].Problem-solving ideas:
By digits entered, find the corresponding letter, then the current existing letters and letter combination.
class Solution {
public:
vector<string> letterCombinations(string digits) {
vector<string> s1,s2;
map<char,vector<string>> mp;
mp['2']={"a","b","c"};
mp['3']={"d","e","f"};
mp['4']={"g","h","i"};
mp['5']={"j","k","l"};
mp['6']={"m","n","o"};
mp['7']={"p","q","r","s"};
mp['8']={"t","u","v"};
mp['9']={"w","x","y","z"};
for(auto &ch:digits){
int size=s1.size();
auto &v=mp[ch];
for(auto &s:v){
for(int i=0;i<size;i++){
string tmp=s1[i]+s;
s2.push_back(tmp);
}
if(size==0) s2.push_back(s);
}
swap(s1,s2);
s2.clear();
}
return s1;
}
};